4-Dodecylbenzenesulfonic acid (DBSA) promoted solvent-free diversity-oriented synthesis of primary carbamates, S-thiocarbamates and ureas

Abstract

A simple and highly efficient solvent-free method for the conversion of alcohols, phenols, thiols and amines to primary carbamates, S-thiocarbamates and ureas in the presence of 4-dodecylbenzenesulfonic acid (DBSA) as a cheap and green Brønsted acid reagent has been described. All products were obtained in good to excellent yields and characterized using FT-IR, ¹H- and ¹³C-NMR, MS and CHNS techniques.

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Introduction

Carbamates, S-thiocarbamates and ureas are an important class of compounds which have been widely used in various areas, including pharmaceuticals, agrochemicals, protection of amino groups in peptide chemistry, and as linkers in combinational chemistry.¹ Furthermore, the role of the carbamate linkage has been extensively studied in structurally diverse natural/semi-synthetic molecules against various diseases, such as antibacterial,^2a,b anti-diabetic,^2c anti-estrogenic,^2d anti-cancer,^2e,f anti-inflammatory,^2g antitumor,^2h anti-Alzheimer,²ⁱ anti-helminthes,²ⁱ anti-osteoporosis,^2j anti-progestational,^2k anti-malarial,^2l antiviral,^2m anti-obesity,²ⁿ anticonvulsant^2o and anti-HIV^2p drugs. S-Thiocarbamates and urea derivatives have usually been used as anti-bacterial,^3a receptor antagonists,^3b anesthetic,^3c pesticide,^3d antiviral^3e and biological receptors inhibitor agents.^3f Besides, these compounds are most noted for their use as commercial herbicides.³

Although numerous procedures have been developed for the synthesis of N-substituted carbamates, S-thiocarbamates and ureas, they are commercially produced by the phosgenation of primary amines, in which highly toxic phosgene was used.⁴ More safe substitution reagents have been introduced such as 1,1,1-trichloromethylformate (diphosgene),⁵ bis-(1,1,1-trichloromethyl) carbonate (triphosgene),⁶ trichloroacetyl chloride,⁷ 1,1-carbonyldiimidazole (CDI),⁸ diethyl carbonates (DEC)⁹ and dimethyl carbonate (DMC).^10a

Moreover, various catalytic systems such as SiO₂,^10b lead(II) nitrate,^10c MCM-41-TBD,^10d ytterbium triflate (Y(OTf)₄),^10e acid functionalized ionic liquids,^10f supported zirconia catalyst,^10g ionic liquids,^10h Cs₂CO₃,¹⁰ⁱ have been reported for the preparation of carbamates from the reaction of DMC with an amine.

Also several interesting methodologies have been developed for the synthesis of carbamates without the application of phosgene as a starting material such as: (a) the oxidative carbonylation of amines, thiols and alcohols with CO in the presence of transition metal compounds such as Pd, Ru, Zn, Ni and Mn as a catalyst,¹¹ (b) the reductive carbonylation of nitro compounds such as nitrobenzene with alcohols and CO in the presence of Ru, Rh or Pd compounds.¹² However, the toxicity of CO and the deactivation of the noble metal catalytic system made this process very uneconomical, (c) conversation of acids to various carbamates in the presence of Me₃P and commercially available chloroformates,¹³ (d) the reaction of CO₂, amines and alcohols in the presence of homogeneous metal catalysts (Sn, Ni, Cs, Ir, Ru)¹⁴ and heterogeneous catalysts (CeO₂, TiO₂–Cr₂O₃/SiO₂ and Cu–Fe/ZrO₂–SiO₂).¹⁵

Another strategy for the synthesis of ureas and carbamates is using Hoffmann, Curtius and Lossen rearrangement through an cyanate intermediate and its trapping with alcohols and amines.^16–20

Various methods for the synthesis of S-alkyl thiocarbamates have been reported.²¹ In one of them, condensation of a thiol with a cyanate affords the corresponding S-thiocarbamate. However, this route was only successful if alkoxy and arylsulfonyl cyanates were employed and the application of cyanates, particularly those of low molecular weight, has been avoided due to their high toxicity.^7,22 Furthermore, the reaction of primary aliphatic amines with S-alkyl chlorothioformates and then the reaction of thiols with the produced carbamoyl chlorides in the presence of a base afforded the corresponding S-thiocarbamate.^7,22a N,N-Disubstituted S-alkyl thiocarbamates have also been prepared from salts of dithiocarbamic acid, which were prepared by the addition of secondary amines to carbon disulfide (CS₂).^7,22a

Many other reports illustrate the intramolecular rearrangement of various derivatives to afford S-alkyl thiocarbamates. However, these rearrangements are extremely limited in starting substrates.²³ Transition metal species containing elements such as palladium, nickel and rhodium have also been employed to promote rearrangement. There are a variety of other methods that are limited to the preparation of complex starting materials.^21a,24

Also a two-step synthesis of a variety of S-alkyl thiocarbamate (primary, secondary and tertiary) has been reported via the reaction of thiols with trichloroacetyl chloride followed by the displacement of the trichloroacetyl group upon treatment with an amine.⁷

There again seems to be only one report in the literature for formation of primary S-thiocarbamates in which the hydration of a variety of organic thiocyanates affords the desired compounds in the presence of hydrogen chloride and concentrated sulfuric acid.^7,25

Most of these methods are employed to produce N-substituted carbamates, S-thiocarbamates and ureas and are not able to be used to synthesize N-unsubstituted ones. The use of cyanate salt in the synthesis of primary carbamates through the reaction with alcohols using various kinds of acidic catalysts, such as trichloroacetic acid, silica supported-sulfuric acid, silica supported-perchloric acid and Al(HSO₄)₃ has been reported.²⁷

4-Dodecylbenzenesulfonic (DBSA), a surfactant that can act as a combined Brønsted acid-surfactant-catalyst (BASC). In the other word, it is able to perform the dual role: (a) as an acid catalyst to activate the substrate molecules and a surfactant to increase the concentration of organic reactants by forming micellar aggregates in water.²⁸ DBSA have been used in chemical synthesis such as synthesis of xanthenes,^29,30 bis(indol-3-yl)alkane derivatives,³¹ carbon–carbon bond forming reactions,³² reaction of homoallyl alcohols and aldehydes in water,³³ N-alkylation of aldoximes,³⁴ synthesis of tetrahydrobenzopyrans,³⁵ dehydration reactions in water,³⁶ Thiol-Michael addition reactions,³⁷ 1,1-diacetates,³⁸ pyrrolo- and indolo[1,2-a]quinoxalines in ethanol³⁹ and cyclotrimerization of acetophenones.³⁰

Herein, we report a new and highly efficient route for the synthesis of N-unsubstituted carbamates 1, S-thiocarbamates 2 and ureas 3 via the treatment of alcohols, thiols and amines 4 with cyanate salts 5 in the presence of 4-dodecylbenzenesulfonic acid (DBSA) 6 as an effective acid under solvent-free condition (Scheme 1).

Scheme 1

Results and discussion

For finding a new and suitable preparation method of primary carbamates, the reaction of phenol with potassium cyanate in the presence of DBSA was chosen as the model reaction and optimization of the reaction parameters was performed and the results were summarized in Table 1. According to these data, using molar ratio 1.5 : 1 : 1.5 among DBSA, phenol and potassium cyanate respectively under solvent-free and 60 °C gave the highest yield of phenyl carbamate in the shortest time (entry 1, Table 1).

Table 1 Optimization of parameters of the reaction phenol with potassium cyanate

Entry	Molar ratio (DBSA : phenol : KNCO)	Solvent	Temperature (°C)	Time (min)	Yield (%)
1	1.5 : 1 : 1.5	—	60	60	90
2	1.5 : 1 : 1.5	—	RT	180	67
3	1 : 1 : 1	—	60	90	78
4	1.2 : 1 : 1.2	—	60	60	84
5	2 : 1 : 2	—	60	60	90
6	1 : 1 : 1.5	—	60	60	75
7	1.5 : 1 : 1	—	60	60	82
8	1.5 : 1 : 1.5	CH3CN	Reflux	60	63
9	1.5 : 1 : 1.5	CH3CO2Et	Reflux	60	65
10	1.5 : 1 : 1.5	CHCl3	Reflux	60	62
11	1.5 : 1 : 1.5	CH2Cl2	Reflux	60	58
12	1.5 : 1 : 1.5	CCl4	Reflux	60	50
13	1.5 : 1 : 1.5	Toluene	Reflux	60	57
14	1.5 : 1 : 1.5	PEG200	Reflux	60	48

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The effect of Brønsted acids such as HCl, H₂SO₄, CCl₃COOH, HClO₄, CF₃COOH, SiO₂–HClO₄, SiO₂–OSO₃H, ClSO₃H, p-TSA were explored on the model reaction instead of DBSA. On the basis of results exhibited in Table 2, the reaction was led in the desired product in the presence of all of acids checked but in lower yields after 60 min at 60 °C. Using sodium and ammonium cyanates in the place of potassium cyanate were not conducted to the better yields.

Table 2 Comparison among efficiency of some other Brønsted acids with DBSA and metal cyanates with potassium cyanate^a

Entry	Catalyst	Cyanate salt	Yield (%)
a Reaction condition: phenol (1 mmol), MOCN (1.5 mmol), DBSA (1.5 mmol), 60 °C, 60 min.
1	HCl (37%)	KOCN	25
2	H2SO4	KOCN	30
3	CCl3COOH	KOCN	70
4	HClO4	KOCN	62
5	CF3COOH	KOCN	54
6	SiO2–HClO4	KOCN	60
7	SiO2–OSO3H	KOCN	63
8	ClSO3H	KOCN	56
9	p-TSA	KOCN	55
10	DBSA	KOCN	90
11	DBSA	NaOCN	83
12	DBSA	NH4OCN	80

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With having the optimized conditions, various alcohols and phenols were treated with potassium cyanate salt in the presence of DBSA at 60 °C to determine efficiency, scope and versatility of the method for one pot and solvent-free synthesis of primary carbamates, which their results were shown in Table 3.

Table 3 Preparation of primary aliphatic and aromatic carbamates^a

Entry	ROH	Product	Time (min)	Yield (%)
a Reaction condition: phenol or alcohol (1 mmol), KOCN (1.5 mmol), DBSA (1.5 mmol), 60 °C.
1			45	83
2			45	88
3			45	83
4			45	90
5			45	84
6			45	90
7			60	65
8			60	71
9			60	70
10			60	67
11			60	52
12			60	65
13			60	62
14			60	58
15			30	89
16			30	88
17			30	80
18			30	79
19			30	85
20			30	83
21			30	76
22			30	52
23			30	84
24			30	87
25			30	90
26			30	87
27			45	82
28			45	77
29			30	68
30			60	NR
31			60	NR
32			60	NR
33			60	NR

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Primary, secondary and tertiary alcohols underwent the carbamate preparation at 60 °C after 30 min in high to moderate yields (Table 3, entries 17–26 and 29) although in the case of tert-butyl alcohol steric hindrance was resulted in lower yield relative to the other class of alcohols (Table 3, entry 22). Phenol and its derivatives with alkyl substitution were also carried out the reaction in high yields after longer reaction time (Table 3, entries 1–7, 27 and 28) except in the case of 2-tert-butyl-4-methylphenol, which suffers from severe steric hindrance of tert-butyl group in the ortho position, which was resulted in lower yield even after longer time (Table 3, entry 7). Phenols with bearing halogen substitutions were also performed the carbamate formation in moderate yields after 60 min (Table 3, entries 8–14) but phenols with strong electron-withdrawing such as NO₂, CN, COOR, and CHO (Table 3, entries 30–33) failed to carrying out the reaction under optimized experimental conditions. Most likely these functional groups decrease the nucleophilicity of the phenol oxygen atom for effective attack. On the other hand, phenols with strong electron-donating substitutions, such as methoxy and phenoxy groups were converted to the corresponding carbamates in high yields in shorter reaction times (30 min) and (Table 3, entries 15 and 16). Both isomers of naphthol were also transformed to the desired carbamates after 45 min in 82 and 77% yields (Table 3, entries 27 and 28).

According to the encouraging results obtained from the synthesis of carbamates, it was decided to apply thiols and amines instead of alcohols and phenols for introducing an efficient and facile method for preparation of S-thiocarbamates and ureas.

Therefore, in order to synthesis of primary aliphatic and aromatic S-thiocarbamates, primary aliphatic and aromatic mercaptans were reacted with potassium cyanate in the presence of DBSA and the obtained data are exhibited in Table 4. According to these results, although all of the aliphatic and primary thiols carried out the corresponding S-thiocarbamate in high to excellent yields in relatively short reaction times but aromatic thiols with electron-releasing substitution underwent the reaction in lower yields than aromatic thiols. Among the aliphatic thiols, thiols with steric hindrance produced the desired products in lower yields (Table 4, entries 12 and 13).

Table 4 Preparation of primary S-thiocarbamates under solvent-free^a at 60 °C

Entry	RSH	Product	Time (min)	Yield (%)
a Reaction condition: thiols (1 mmol), KOCN (1.5 mmol), DBSA (1.5 mmol), 60 °C.
1			30	93
2			30	94
3			30	89
4			30	85
5			30	93
6			30	84
7			30	91
8			30	89
9			30	90
10			30	92
11			30	90
12			30	83
13			30	81
14			30	86

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Preliminary examination on the preparation of ureas from potassium cyanate and primary amines in the presence of DBSA at 60 °C under solvent free conditions, as the same as optimized condition for synthesis of carbamates and S-thiocarbamates, was led to the desired products in lower yields. But raising the reaction temperature up to 80 °C resulted in high to excellent yields. Therefore, variety of primary aromatic amines bearing electron-releasing and electron-withdrawing substituents, primary and secondary aliphatic amines were explored under the new optimized conditions for production of the corresponding ureas, which their information were summarized in Table 5. As the same as for carbamates and S-thiocarbamates, among primary aromatic amine those with electron-donating substitutions underwent the reaction more efficient (Table 5, entries 2 and 4). Except in the case of 4-dimethylaminoaniline, in which dimethylamino group, as an electron-donating substituent, is converted to an electron-attracting one, dimethylammonium salt, in the presence of DBSA (Table 5, entry 5). Aliphatic amines, including primary and secondary, carried out this reaction to provide the title products in high yields (Table 5, entries 7–9).

Table 5 Preparation of ureas under solvent-free^a at 80 °C

Entry	RNH2	Product	Time (min)	Yield (%)
a Reaction condition: amines (1 mmol), KOCN (1.5 mmol), DBSA (1.5 mmol), 80 °C.
1			45	90
2			45	92
3			45	87
4			45	85
5			45	90
6			45	81
7			45	93
8			45	83
9			45	86

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According to the information in the literature^26,40 and the results obtained in this study, a plausible mechanism for preparation of the title compounds might be as follows. In the first step, potassium cyanate is protonated by DBSA to produce isocyanic acid that undergoes protonation again and then will be attacked by the existence nucleophile in the media.

According to the plausible mechanism, important features of DBSA, which make it suitable for synthesis of the title compounds, are: (a) its acidic power, which is suitable to produce isocyanic acid and subsequently its protonated form to be attacked by a nucleophile, (b) its viscosity, which prevents escape of isocyanic acid after it is produced therefore rendering a sufficient concentration of isocyanic acid in the reaction media, and (c) its long lipophilic hydrocarbon chain, which provides an organic environment for the reactants.

To checking recognize the applicability of our method at large scales, we examined some reactions in scales of 50 and 200 mmol. The results were summarized in Table 6. As shown in Tables 3–5, the reactions were successfully performed at large scales without significant loss of the yields.

Table 6 The large scale preparation of phenyl carbamate, phenyl S-thiocarbamate and 1-phenylurea under solvent-free

Product	Phenol, thiophenol or aniline (mmol)	Time (min)	Yield (%)
	1	45	83
	50	100	80
	200	100	81
	1	30	93
	50	60	89
	200	60	90
	1	45	90
	50	100	88
	200	100	87

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Experimental

General

All chemicals used in this work were purchased from the Merck, Fluka Chemical Company in high purity. The products were characterized by comparison of their spectral and physical data such as NMR, FT-IR, MS, CHNS and melting point with available literature data. ¹H and ¹³C-NMR spectra were recorded with Bruker Avance DPX 250 MHz instruments with Me₄Si or solvent resonance as the internal standard (¹H-NMR: Me₄Si at 0 ppm, DMSO at δ = 3.35 ppm; ¹³C-NMR: Me₄Si at 0 ppm, DMSO at δ = 39.42 ppm). ¹H-NMR spectroscopic data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, quint = quintet, sext = sextet, sept = septet, br. = broad, m = multiplet), coupling constants (Hz), and integration. Fourier transform infrared (FTIR) spectra were obtained using a Shimadzu FT-IR 8300 spectrophotometer. The C, H, N and S elemental analyses were carried out by the using a Thermofinnigan Flash EA-1112 CHNSO rapid elemental analyzer. The mass spectra were recorded on a Shimadzu GC-MS QP 1000 EX instrument. Melting points were recorded by Electrothermal 9100.

General procedure for the synthesis of primary carbamates

To a mixture of alcohol or phenol (1.0 mmol) and potassium cyanate (1.5 mmol, 0.121 g) in a mortar, DBSA (1.5 mmol, 0.489 g) was added and the mixture was pulverized until a uniform mixture was formed. Obtained mixture was kept in an oven at a constant temperature (60 °C) for appropriate time (Table 1). During this time, the mixture was grinded for ten seconds every each 5 minutes and the completion of reaction was monitored with TLC using n-hexane : ethyl acetate 9 : 1 as an eluent. After completion of the reaction, obtained powder was transferred to a beaker, CH₂Cl₂ (15 mL) and saturated aqueous solution of NaHCO₃ (15 mL) were added and organic layer was extracted, washed with water (2 × 15 mL), dried over anhydrous Na₂SO₄, filtered, and concentrated to afford the crude product. The recrystallization from diethyl ether gave pure product.

General procedure for the synthesis of primary S-thiocarbamates

To a mixture of thiols (1.0 mmol) and potassium cyanate (1.5 mmol, 0.121 g) in a mortar, DBSA (1.5 mmol, 0.489 g) was added and the mixture was pulverized until a uniform mixture was formed. Obtained mixture was kept in an oven at a constant temperature (60 °C) for appropriate time (Table 2). During this time, the mixture was grinded for ten seconds every each 5 minutes and the completion of reaction was monitored with TLC using n-hexane : ethyl acetate 9 : 1 as an eluent. After completion of the reaction, obtained powder was transferred to a beaker, CH₂Cl₂ (15 mL) and saturated aqueous solution of NaHCO₃ (15 mL) were added and organic layer was extracted, washed with water (2 × 15 mL), dried over anhydrous Na₂SO₄, filtered, and concentrated to afford the crude product. The recrystallization from diethyl ether gave pure product.

General procedure for synthesis of ureas

To a mixture of amines or anilines (1.0 mmol), and potassium cyanate (1.5 mmol, 0.121 g) in a mortar, DBSA (1.5 mmol, 0.489 g) was added and the mixture was pulverized until a uniform mixture was formed. Obtained mixture was kept in an oven at a constant temperature (80 °C) for appropriate time (Table 3). During this time, the mixture was grinded for ten seconds every each 5 minutes and the completion of reaction was monitored with TLC using n-hexane : ethyl acetate 9 : 1 as an eluent. After completion of the reaction, obtained powder was transferred to a beaker, CH₂Cl₂ (15 mL) and saturated aqueous solution of NaHCO₃ (15 mL) were added and organic layer was extracted, washed with water (2 × 15 mL), dried over anhydrous Na₂SO₄, filtered, and concentrated to afford the crude product. The recrystallization from diethyl ether gave pure product.

Phenyl carbamate. Reaction afforded white crystals (83% yield), mp = 140–142 °C (lit.,²⁷ 141–143 °C). IR (KBr); 3410 (s), 3335 (s), 3271 (s), 3189 (s), 3071 (s), 1707 (vs), 1614 (s), 1486 (s), 1372 (vs), 1201 (vs), 1162 (s), 1069 (m), 1003 (m), 1022 (m), 973 (vs), 915 (w), 838 (m), 762 (s), 696 (vs), 585 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 6.89 (s, br, 2H, NH), 7.07 (d, J = 7.5 Hz, 2H), 7.17 (t, J = 7.5 Hz, 1H), 7.35 (t, J = 7.5 Hz, 2H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 121.88, 124.77, 129.11, 151.02, 154.76. MS calcd m/z 137.14, found 137. Anal. calcd for C₇H₇NO₂: C, 61.31; H, 5.14; N, 10.21%. Found: C, 61.28; H, 5.16; N, 10.32%.

2-Methylphenyl carbamate. Reaction afforded white crystals (88% yield), mp = 132–134 °C (lit.,²⁷ 132–135 °C). IR (KBr); 3416 (s), 3333 (s), 3272 (s), 3192 (m), 3032 (vw), 1710 (vs), 1613 (m), 1492 (m), 1370 (vs), 1227 (vs), 1180 (vs), 1114 (s), 1041 (m), 972 (vs), 868 (w), 839 (w), 775 (m), 752 (s), 719 (m), 678 (w), 600 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.12 (s, 3H), 6.85 (s, br, 2H, NH), 7.13 (m, 4H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 15.65, 122.46, 125.09, 126.64, 130.36, 130.62, 149.50, 134.57. MS calcd m/z 151.16, found 151. Anal. calcd for C₈H₉NO₂: C, 63.56; H, 6.00; N, 9.27%. Found: C, 63.48; H, 6.06; N, 9.32%.

3-Methylphenyl carbamate. Reaction afforded white crystals (83% yield), mp = 137–138 °C (lit.,²⁷ 137–139 °C). IR (KBr); 3414 (m), 3334 (m), 3274 (m), 3192 (m), 2919 (m), 1716 (s), 1612 (m), 1487 (m), 1374 (s), 1242 (s), 1150 (s), 1082 (m), 979 (vs), 915 (s), 806 (s), 776 (m), 754 (s), 702 (s), 679 (v), 563 (vs), 445 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.30 (s, 3H), 6.85–7.26 (m, 6H). ¹³C-NMR (60 MHz, 298 K, DMSO-d6), δ ppm; 20.74, 118.82, 122.35, 125.38, 128.75, 138.66, 150.99, 154.82. MS calcd m/z 151.16, found 151. Anal. calcd for C₈H₉NO₂: C, 63.56; H, 6.00; N, 9.27%. Found: C, 63.52; H, 6.02; N, 9.31%.

4-Methylphenyl carbamate. Reaction afforded white crystals (90% yield), mp = 133–134 °C (lit.,²⁷ 134–136 °C). IR (KBr); 3406 (s), 3334 (s), 3276 (s), 2923 (w), 1710 (s), 1610 (w), 1508 (w), 1380 (s), 1218 (s), 1165 (w), 1019 (w), 978 (s), 857 (m), 812 (w), 766 (m), 665 (w), 620 (w), 549 (s), 430 (m) cm⁻¹. ¹H-NMR (300 MHz, 298 K, DMSO-d6), δ ppm; 2.28 (s, 3H), 6.91 (d, J = 8.5 Hz, 2H), 7.15 (d, J = 8.5 Hz, 2H), 8.98 (s, br, 1H, NH), 9.16 (s, br, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 20.36, 122.44, 129.39, 132.66, 150.99, 190.56. MS calcd m/z 151.16, found 151. Anal. calcd for C₈H₉NO₂: C, 63.56; H, 6.00; N, 9.27%. Found: C, 63.54; H, 6.03; N, 9.29%.

2,6-Dimethylphenyl carbamate. Reaction afforded white crystals (84% yield), mp = 182–184 °C. IR (KBr); 3417 (m), 3334 (w), 3272 (m), 3192 (w), 3044 (m), 2947 (m), 2919 (m), 2857 (w), 1709 (s), 1614 (m), 1487 (s), 1383 (s), 1265 (m), 1187 (s), 1118 (m), 1091 (m), 990 (vs), 836 (m), 773 (vs), 724 (m), 618 (vs), 550 (vw), 472 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.09 (s, 6H), 6.83 (s, br, 1H, NH), 7.02 (m, 3H), 7.18 (s, br, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 15.82, 124.91, 128.12, 130.55, 148.13, 154.19. MS calcd m/z 165.19, found 165. Anal. calcd for C₉H₁₁NO₂: C, 65.44; H, 6.71; N, 8.48%. Found: C, 65.39; H, 6.73; N, 8.49%.

3,4-Dimethylphenyl carbamate. Reaction afforded white crystals (90% yield), mp = 130–132 °C. IR (KBr); 3414 (m), 3334 (v), 3270 (m), 3197 (m), 3032 (v), 2970 (m), 2943 (m), 2922 (m), 1711 (s), 1615 (m), 1499 (m), 1451 (v), 1372 (s), 1274 (m), 1247 (m), 1194 (m), 1154 (m), 1013 (vs), 980 (s), 922 (m), 874 (m), 837 (m), 782 (m), 744 (vw), 702 (w), 676 (w), 573 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.17 (s, 6H), 6.74–7.08 (m, 5H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 18.62, 19.28, 118.91, 122.75, 129.75, 133.55, 137.02, 148.91, 154.98. MS calcd m/z 165.19, found 165. Anal. calcd for C₉H₁₁NO₂: C, 65.44; H, 6.71; N, 8.48%. Found: C, 65.41; H, 6.74; N, 8.51%.

2-tert-Butyl-4-methylphenyl carbamate. Reaction afforded white crystals (65% yield), mp = 142–143 °C (lit.,²⁷ 143–144 °C). IR (KBr); 3455 (s), 3334 (w), 3255 (m), 3192 (w), 3041 (m), 2953 (s), 2909 (s), 2848 (s), 1730 (vs), 1613 (s), 1575 (s), 1497 (s), 1357 (s), 1278 (m), 1206 (s), 1141 (v), 1091 (s), 976 (vs), 907 (v), 878 (v), 840 (s), 814 (m), 791 (m), 772 (m), 729 (v), 675 (v), 591 (v), 492 (m) cm⁻¹.¹H-NMR (250 MHz, 293 K, DMSO-d6), δ ppm; 1.29 (s, 9H), 2.25 (s, 3H), 6.82 (m, 4H), 7.14 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 20.67, 29.99, 34.01, 124.40, 126.82, 126.92, 133.39, 140.52, 147.21, 154.96. MS calcd m/z 207.27, found 207. Anal. calcd for C₁₂H₁₇NO₂: C, 69.54; H, 8.27; N, 6.76%. Found: C, 69.47; H, 8.28; N, 6.81%.

4-Flourophenyl carbamate. Reaction afforded white crystals (71% yield), mp = 131–133 °C. IR (KBr); 3408 (s), 3327 (m), 3274 (s), 1707 (vs), 1609 (s), 1494 (m), 1378 (s), 1193 (vs), 1090 (w), 976 (vs), 864 (s), 831 (m), 779 (s), 547 (vs) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 6.95 (s, br, 1H, NH), 7.10–7.23 (m, 5H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 115.92–116.29 (J = 23.1 Hz), 124.01–124.14 (J = 8.6 Hz), 147.61–147.65 (J = 1.9 Hz), 155.26, 157.60–161.42 (J = 238.9 Hz). MS calcd m/z 155.04, found 155. Anal. calcd for C₇H₆FNO₂: C, 54.20; H, 3.90; N, 9.03%. Found: C, 54.17; H, 3.97; N, 9.11%.

4-Chlorophenyl carbamate. Reaction afforded white crystals (70% yield), mp = 168–170 °C. IR (KBr); 3413 (m), 3334 (w), 3272 (m), 3192 (w), 1706 (vs), 1595 (s), 1478 (s), 1365 (s), 1225 (vs), 1097 (s), 1013 (m), 970 (vs), 859 (m), 827 (s), 763 (m), 736 (m), 501 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 6.99 (s, br, 1H, NH), 7.33 (d, J = 7.5 Hz, 2H), 7.26 (s, br, 1H, NH), 7.42 (d, J = 7.5 Hz, 2H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 123.75, 128.84, 129.00, 149.82, 154.38. MS calcd m/z 171.58, found 171. Anal. calcd for C₇H₆ClNO₂: C, 49.00; H, 3.52; N, 8.16%. Found: C, 48.67; H, 3.58; N, 8.21%.

2-Chlorophenyl carbamate. Reaction afforded white crystals (67% yield), mp = 157–159 °C. IR (KBr); 3407 (s), 3326 (m), 3274 (s), 1722 (s), 1599 (s), 1479 (m), 1360 (s), 1262 (w), 1218 (vs), 1065 (m), 1032 (w), 968 (vs), 832 (w), 766 (vs), 736 (s), 686 (w), 532 (s) cm⁻¹.¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 7.02 (s, br, 1H, NH), 7.22–7.33 (3H, 1H, NH), 7.50 (d, J = 7.75 Hz, 1H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 124.72, 126.60, 126.68, 128.05, 129.79, 147.02, 153.70. MS calcd m/z 171.58, found 171. Anal. calcd for C₇H₆ClNO₂: C, 49.00; H, 3.52; N, 8.16%. Found: C, 48.63; H, 3.57; N, 8.19%.

2,4-Dichlorophenyl carbamate. Reaction afforded white crystals (52% yield), mp = 147–149 °C. IR (KBr); 3782 (m), 3698 (w), 3406 (s), 3331 (w), 3265 (m), 1710 (vs), 1612 (s), 1487 (s), 1371 (s), 1213 (vs), 1085 (s), 1013 (m), 980 (vs), 859 (s), 806 (m), 779 (w), 736 (m), 510 (s) cm⁻¹.¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 7.01 (s, br, 1H, NH), 7.22–7.51 (m, 4H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 124.71, 126.59, 126.66, 128.04, 129.79, 147.03, 153.70. MS calcd m/z 206.97, found 207. Anal. calcd for C₇H₅Cl₂NO₂: C, 40.81; H, 2.45; N, 6.80%. Found: C, 40.67; H, 2.48; N, 6.81%.

4-Bromophenyl carbamate. The reaction afforded white crystals (65% yield), mp = 138–140 °C (lit.,²⁷ 139–142 °C). IR (KBr); 3782 (m), 3697 (w), 3405 (s), 3324 (w), 3254 (w), 3203 (m), 1704 (s), 1602 (s), 1376 (vs), 1242 (s), 1210 (m), 1160 (s), 991 (s), 898 (w), 861 (w), 825 (w), 778 (w), 739 (w), 543 (s), 476 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 6.98 (br, s, 1H), 7.07 (d, J = 8.7 Hz, 2H), 7.25 (br, s, 1H), 7.54 (d, J = 8.7 Hz, 2H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 120.91, 124.19, 131.95, 148.56, 154.30. MS calcd m/z 214.96, found 215. Anal. calcd for C₇H₆BrNO₂: C, 38.92; H, 2.80; N, 6.48%. Found: C, 38.83; H, 2.84; N, 6.51%.

2-Bromophenyl carbamate. The reaction afforded white crystals (62% yield), mp = 156–158 °C. IR (KBr); 3416 (s), 3338 (s), 3270 (s), 3190 (s), 3084 (m), 1710 (vs), 1617 (s), 1498 (s), 1368 (vs), 1287 (w), 1238 (m), 1198 (vs), 1148 (vw), 1092 (m), 1014 (w), 972 (s), 942 (w), 866 (s), 858 (m), 831 (s), 779 (s), 708 (m), 664 (m), 548 (s), 515 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 7.02 (br, s, 1H), 7.12–7.40 (m, 4H), 7.64 (d, J = 8.0 Hz, 1H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 116.46, 124.74, 126.98, 128.66, 132.78, 148.23, 153.70. MS calcd m/z 214.96, found 215. Anal. calcd for C₇H₆BrNO₂: C, 38.92; H, 2.80; N, 6.48%. Found: C, 38.85; H, 2.83; N, 6.53%.

4-Iodophenyl carbamate. Reaction afforded white crystals (58% yield), mp = 166–168 °C. IR (KBr); 3386 (s), 3334 (s), 3274 (s), 3190 (s), 3167 (m), 1710 (vs), 1611 (m), 1474 (s), 1448 (m), 1364 (vs), 1262 (s), 1217 (vs), 1127 (vw), 1111 (m), 1049 (s), 1027 (s), 987 (vw), 966 (vs), 946 (vw), 930 (vw), 831 (vs), 762 (vs), 729 (s), 698 (vw), 675 (m), 652 (m), 595 (s), 523 (m), 471 (w), 446 (w), 418 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 6.59 (s, br, 1H, NH), 6.90 (s, 2H), 7.20 (s, br, 1H, NH), 7.66 (s, 2H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 118.12, 124.47, 137.84, 150.91, 154.32. MS calcd m/z 263.03, found 263. Anal. calcd for C₇H₆INO₂: C, 31.96; H, 2.30; N, 5.33%. Found: C, 31.89; H, 2.34; N, 5.35%.

4-Methoxyphenyl carbamate. Reaction afforded white crystals (89% yield), mp = 128–130 °C. IR (KBr); 3410 (s), 3340 (s), 3270 (s), 3208 (s), 3065 (vw), 3016 (vw), 2974 (m), 2938 (m), 2844 (m), 1764 (w), 1714 (vs), 1624 (w), 1595 (vw), 1507 (s), 1459 (m), 1445 (w), 1376 (vs), 1298 (m), 1246 (s), 1206 (vs), 1186 (s), 1127 (w), 1102 (m), 1030 (s), 1008 (m), 978 (s), 954 (m), 933 (vw), 848 (s), 821 (s), 784 (m), 765 (m), 726 (w), 705 (w), 670 (w), 564 (s), 524 (s), 419 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 3.71 (s, 3H), 6.87 (d, J = 9 Hz, 2H), 6.99 (d, J = 9 Hz, 2H), 7.09 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 55.27, 114.05, 122.72, 144.45, 155.16, 156.18. MS calcd m/z 167.16, found 167. Anal. calcd for C₈H₉NO₃: C, 57.48; H, 5.43; N, 8.38%. Found: C, 57.41; H, 5.47; N, 8.45%.

O-4-Phenoxyphenyl carbamate. Reaction afforded white crystals (88% yield), mp = 103–105 °C. IR (KBr); 3412 (m), 3271 (m), 3156 (m), 1700 (s), 1602 (s), 1504 (vs), 1344 (m), 1294 (w), 1211 (vs), 1094 (w), 1074 (w), 1010 (w), 978 (m), 875 (m), 850 (s), 815 (m), 752 (s), 691 (m), 629 (w), 501 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 6.85 (m, 7H), 7.92 (m, 2H), 9.84 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 116.19, 116.75, 120.89, 122.07, 129.70, 147.56, 151.53, 154.04, 158.41. MS calcd m/z 229.23, found 229. Anal. calcd for C₁₃H₁₁NO₃: C, 68.11; H, 4.84; N, 6.11%. Found: C, 68.08; H, 4.88; N, 6.15%.

Methyl carbamate. Reaction afforded white crystals (80% yield), mp = 51–53 °C (lit.,²⁷ 52–54 °C). IR (KBr); 3443 (m), 3328 (m), 3209 (m), 2966 (m), 1704 (s), 1467 (m), 1367 (s), 1078 (vs), 881 (s), 787 (vs), 709 (m), 518 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 3.45 (s, 3H), 6.42 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 50.83, 157.16. MS calcd m/z 75.05, found 75. Anal. calcd for C₂H₅NO₂: C, 32.00; H, 6.71; N, 18.66%. Found: C, 31.88; H, 6.78; N, 18.75%.

Ethyl carbamate. Reaction afforded white crystals (79% yield), mp = 45–46 °C (lit.,²⁷ 46–48 °C). IR (KBr); 3416 (m), 3217 (w), 2989 (m), 1704 (vs), 1414 (m), 1340 (s), 1236 (s), 1078 (s), 1022 (w), 835 (m), 785 (s), 595 (s), 472 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 1.11 (t, J = 7.0 Hz, 3H), 3.90 (q, J = 7.0 Hz, 2H), 6.38 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 15.56, 59.09, 156.73. MS calcd m/z 89.09, found 89. Anal. calcd for C₃H₇NO₂: C, 40.44; H, 7.92; N, 15.72%. Found: C, 40.38; H, 7.98; N, 15.75%.

2-Propyl carbamate. Reaction afforded white crystals (85% yield), mp = 88–90 °C (lit.,²⁷ 89–91 °C). IR (KBr); 3429 (vw), 3218 (v), 2985 (m), 2985 (s), 1684 (s), 1417 (s), 1320 (s), 1108 (s), 1046 (s), 901 (m), 825 (m), 793 (s), 600 (vs), 460 (m), 412 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6) δ ppm; 1.12 (d, J = 6.3 Hz, 6H), 4.67 (h, J = 6.3 Hz, 1H), 6.33 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 21.99, 66.02, 156.36. MS calcd m/z 103.12, found 103. Anal. calcd for C₄H₉NO₂: C, 46.59; H, 8.80; N, 13.58%. Found: C, 46.58; H, 8.78; N, 13.65%.

1-Butyl carbamate. Reaction afforded white crystals (83% yield), mp = 53–54 °C (lit.,²⁷ 53–55 °C). IR (KBr); 3417 (m), 3200 (m), 2962 (m), 2874 (m), 1696 (s), 1435 (m), 1339 (m), 1254 (m), 1121 (w), 1080 (vs), 943 (m), 887 (vw), 788 (m), 740 (w), 638 (s), 556 (s), 438 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 0.86 (t, J = 7.5 Hz, 3H), 1.28 (m, 2H), 1.50 (m, 2H), 3.87 (t, J = 5.0 Hz, 2H), 6.38 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 13.51, 18.54, 30.69, 62.91, 156.83. MS calcd m/z 117.15, found 117. Anal. calcd for C₅H₁₁NO₂: C, 51.26; H, 9.46; N, 11.96%. Found: C, 51.18; H, 9.48; N, 12.05%.

2-Butyl carbamate. Reaction afforded white crystals (76% yield), mp = 92–93 °C (lit.,²⁷ 93–94 °C). IR (KBr); 3418 (w), 3339 (m), 3218 (m), 2986 (s), 1692 (vs), 1416 (s), 1322 (s), 1246 (s), 1182 (m), 1110 (vs), 1048 (vs), 903 (m), 824 (w), 793 (m), 710 (w), 604 (s), 463 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 0.56 (t, J = 7.5 Hz, 3H), 0.76 (d, J = 6.3 Hz, 3H), 1.03–1.09 (m, 2H), 4.92 (m, 1H), 7.91 (s, br, 1H, NH), 8.25 (s, br, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 9.51, 19.60, 28.54, 70.52, 156.60. MS calcd m/z 117.15, found 117. Anal. calcd for C₅H₁₁NO₂: C, 51.26; H, 9.46; N, 11.96%. Found: C, 51.22; H, 9.49; N, 12.03%.

tert-Butyl carbamate. Reaction afforded white crystals (52% yield), mp = 106–107 °C (lit.,²⁷ 106–108 °C). IR (KBr); 3430 (s), 3341 (s), 3264 (s), 3216 (s), 2961 (s), 2877 (m), 1696 (vs), 1617 (vw), 1458 (m), 1474 (w), 1420 (s), 1383 (s), 1356 (s), 1336 (w), 1300 (m), 1244 (m), 1186 (w), 1164 (w), 1120 (m), 1077 (vs), 968 (m), 931 (m), 915 (m), 832 (w), 785 (s), 722 (m), 586 (s), 456 (w), 436 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 1.44 (s, 9H), 6.19 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 21.97, 66.02, 156.36. MS calcd m/z 117.15, found 117. Anal. calcd for C₅H₁₁NO₂: C, 51.26; H, 9.46; N, 11.96%. Found: C, 51.19; H, 9.52; N, 12.07%.

Cyclohexyl carbamate. Reaction afforded white crystals (84% yield), mp = 108–109 °C (lit.,²⁷ 108–110 °C). IR (KBr); 3441 (s), 3324 (s), 3264 (s), 3206 (s), 2940 (s), 2865 (s), 1698 (vs), 1616 (m), 1454 (m), 1406 (vs), 1362 (m), 1345 (m), 1312 (m), 1257 (w), 1196 (w), 1155 (w), 1108 (w), 1093 (vw), 1054 (vs), 1028 (m), 931 (w), 915 (w), 900 (vw), 890 (w), 842 (w), 805 (vw), 788 (s), 693 (m), 677 (vw), 570 (s), 501 (w), 463 (w), 442 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 1.19–1.33 (m, 5H), 1.46 (m, 1H), 1.63–1.77 (m, 4H), 4.38 (t, J = 5.0 Hz, 2H), 6.33 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 23.47, 24.92, 31.73, 71.13, 156.28. MS calcd m/z 143.18, found 143. Anal. calcd for C₇H₁₃NO₂: C, 58.72; H, 9.15; N, 9.78%. Found: C, 58.68; H, 9.19; N, 9.85%.

(−) Methyl carbamate. Reaction afforded white crystals (87% yield), mp = 165–166 °C (lit.,²⁷ 166–168 °C). [α]¹⁷_D −125 °C (0.06, CDCl₃). IR (KBr); 3444 (s), 3331 (m), 3263 (m), 3208 (m), 2954 (s), 2873 (m), 1688 (vs), 1612 (s), 1408 (vs), 1341 (m), 1184 (w), 1048 (vs), 916 (w), 842 (vw), 787 (m), 706 (s), 570 (vs) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6) δ ppm; 0.72 (d, J = 8.5 Hz, 3H), 0.86 (m, 7H), 1.03 (m, 2H), 1.24 (m, 1H), 1.38 (m, 1H), 1.44–1.52 (m, 1H), 1.60 (m, 2H), 1.83–1.92 (m, 2H), 4.35 (td, J = 10.75 Hz, J = 4.25 Hz, 1H), 6.33 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 16.22, 20.49, 21.91, 23.02, 25.63, 30.86, 33.80, 41.27, 46.81, 72.26, 156.52. MS calcd m/z 199.29, found 199. Anal. calcd for C₁₁H₂₁NO₂: C, 66.29; H, 10.62; N, 7.03%. Found: C, 66.21; H, 10.68; N, 7.14%.

2-Phenethyl carbamate. Reaction afforded white crystals (90% yield), mp = 97–98 °C. IR (KBr); 3429 (s), 3331 (m), 3274 (w), 2965 (s), 1694 (vs), 1412 (vs), 1343 (s), 1240 (m), 1079 (vs), 1046 (m), 752 (s), 702 (vs), 645 (m), 570 (m), 497 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.83 (t, J = 7.0 Hz, 2H), 4.10 (t, J = 7.0 Hz, 2H), 6.46 (s, br, 2H, NH), 7.19–7.29 (m, 5H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 34.88, 63.90, 126.17, 128.25, 128.77, 138.26, 156.65. MS calcd m/z 165.19, found 165. Anal. calcd for C₉H₁₁NO₂: C, 65.44; H, 6.71; N, 8.48%. Found: C, 65.38; H, 6.76; N, 8.52%.

1-Phenethyl carbamate. Reaction afforded white crystals (87% yield), mp = 72–75 °C. IR (KBr); 3422 (s), 3330 (m), 3216 (w), 2985 (s), 1689 (vs), 1405 (s), 1313 (m), 1241 (s), 1058 (vs), 851 (w), 764 (s), 698 (vs), 595 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 1.40 (d, J = 6.7 Hz, 3H), 5.62 (q, J = 4.5 Hz, 1H), 6.53 (s, br, 2H, NH), 7.30–7.33 (m, 5H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 22.50, 70.73, 125.56, 127.26, 128.22, 142.80, 156.09. MS calcd m/z 165.19, found 165. Anal. calcd for C₉H₁₁NO₂: C, 65.44; H, 6.71; N, 8.48%. Found: C, 65.35; H, 6.78; N, 8.55%.

Naphthalen-1-yl carbamate. Reaction afforded white crystals (82% yield), mp = 177–179 °C (lit.,²⁷ 178–180 °C). IR (KBr); 3430 (m), 3040 (w), 1702 (s), 1606 (m), 1358 (s), 1260 (s), 1226 (s), 1154 (m), 1085 (s), 1045 (m), 961 (w), 805 (m), 777 (vs), 556 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6) δ ppm; 7.05 (br d, 1H), 7.26 (d, J = 7.5 Hz, 1H), 7.47–7.57 (m, 4H), 7.78 (d, J = 7.6 Hz, 1H), 7.88–7.95 (m, 2H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6) δ ppm; 118.55, 121.06, 124.97, 125.67, 126.31(2C), 127.29, 127.83, 134.0, 146.70, 154.89. Anal. calcd for C₁₁H₉NO₂: C, 70.58; H, 4.85; N, 7.48%. Found: C, 70.48; H, 4.93; N, 7.50%.

Naphthalen-2-yl carbamate. Reaction afforded white crystals (77% yield), mp = 156–158 °C (lit.,²⁷ 157–158 °C). IR (KBr); 3408 (m), 3338 (w), 3272 (m), 3197 (vw), 1706 (vs), 1613 (m), 1483 (m), 1382 (s), 1211 (vs), 1066 (w), 1011 (w), 979 (m), 856 (m), 801 (w), 827 (w), 502 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6) δ (ppm); 6.98 (br s, 1H, NH), 7.28 (dd, J = 8.7, 2.5 Hz, 2H), 7.45–7.51 (m, 2H), 7.61 (d, J = 2.5 Hz, 1H), 7.86–7.92 (m, 3H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6) δ ppm; 118.26, 122.10, 125.31, 126.40, 127.26, 127.51, 128.85, 130.51, 133.36, 148.72, 154.90. MS calcd m/z 187.19, found 187. Anal. calcd for C₁₁H₉NO₂: C, 70.58; H, 4.85; N, 7.48%. Found: C, 70.51; H, 4.92; N, 7.51%.

Allyl carbamate. The reaction afforded white crystals (68% yield), mp = 18–20 °C (lit.,²⁷ 19–21 °C). IR (KBr); 3425 (s), 3233 (s), 3148 (s), 2961 (s), 1732 (vs), 1553 (m), 1508 (w), 1429 (w), 1406 (m), 1539 (w), 1360 (m), 1332 (m), 1238 (vs), 1165 (w), 1141 (w), 1108 (s), 1068 (w), 999 (m), 942 (s), 846 (s), 775 (vs), 670 (vw), 657 (vw), 610 (m), 738 (s), 488 (w), 467 (w), 458 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 4.47 (d, J = 5.5 Hz, 2H), 5.20 (dd, J = 10.5 Hz, J = 1.2 Hz, 1H), 5.31 (dd, J = 17.2 Hz, J = 1.7 Hz, 1H), 5.87–6.02 (m, 1H), 6.56 (br, 2H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 65.26, 117.88, 132.39, 153.54. MS calcd m/z 101.05, found 101. Anal. calcd for C₄H₇NO₂: C, 47.52; H, 6.98; N, 13.85%. Found: C, 47.41; H, 7.02; N, 13.91%.

Phenyl S-thiocarbamate. Reaction afforded white crystals (93% yield), mp = 97–99 °C (lit.,²⁹ 96–98 °C). IR (KBr); 3386 (s), 3328 (m), 3290 (s), 3234 (s), 3174 (s), 3060 (w), 1655 (vs), 1610 (s), 1476 (m), 1458 (m), 1442 (m), 1370 (w), 1282 (vs), 1141 (s), 1098 (m), 1068 (m), 1026 (m), 1002 (w), 922 (m), 843 (w), 750 (vs), 710 (vs), 685 (vs), 619 (w), 532 (vs), 471 (s), 446 (vw) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 7.38 (m, 5H), 7.66 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 128.61, 128.79, 134.79, 149.87, 164.93. MS calcd m/z 153.20, found 153. Anal. calcd for C₇H₇NOS: C, 54.88; H, 4.61; N, 9.14; S, 20.93%. Found: C, 54.75; H, 4.64; N, 9.19; S, 20.97%.

4-Methylphenyl S-thiocarbamate. Reaction afforded white crystals (94% yield), mp = 174–176 °C (lit.,²⁹ 175 °C). IR (KBr); 3410 (s), 3317 (s), 3297 (s), 3175 (s), 3055 (w), 3020 (vw), 2922 (m), 2862 (w), 1647 (vs), 1611 (s), 1492 (m), 1404 (w), 1364 (w), 1316 (vs), 1207 (m), 1180 (m), 1105 (m), 1020 (vw), 844 (m), 810 (s), 707 (m), 688 (s), 638 (vw), 606 (s), 527 (vs), 474 (vw), 463 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.29 (s, 3H), 7.18 (d, J = 8.0 Hz, 2H), 7.29 (d, J = 8.0 Hz, 2H), 7.60 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 20.76, 125.54, 129.46, 135.01, 138.09, 165.37. MS calcd m/z 167.23, found 167. Anal. calcd for C₈H₉NOS: C, 57.46; H, 5.42; N, 8.38; S, 19.17%. Found: C, 57.55; H, 5.34; N, 8.47; S, 19.29%.

4-Chlorophenyl S-thiocarbamate. Reaction afforded white crystals (89% yield), mp = 175–177 °C (lit.,²⁹ 176 °C). IR (KBr); 3407 (s), 3295 (s), 3189 (s), 3078 (w), 1648 (vs), 1612 (s), 1475 (s), 1388 (s), 1321 (s), 1264 (w), 1172 (w), 1111 (m), 1084 (s), 1013 (m), 968 (w), 879 (vw), 824 (vs), 787 (m), 748 (m), 738 (m), 704 (vw), 689 (m), 649 (vw), 614 (m), 568 (m), 514 (m), 484 (m), 464 (m), 434 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 7.35 (d, J = 8.5 Hz, 2H), 7.56 (d, J = 8.5 Hz, 2H), 7.78 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 128.18, 128.76, 133.68, 136.54, 164.40. MS calcd m/z 187.65, found 187. Anal. calcd for C₇H₆ClNOS: C, 44.80; H, 3.22; N, 7.46; S, 17.09%. Found: C, 44.69; H, 3.24; N, 7.53; S, 16.89%.

4-Bromophenyl S-thiocarbamate. Reaction afforded white crystals (85% yield), mp = 183–185 °C (lit.,²⁹ 184 °C). IR (KBr); 3406 (s), 3314 (s), 3287 (s), 3174 (s), 3075 (m), 1644 (vs), 1611 (s), 1470 (s), 1449 (vw), 1389 (m), 1365 (vw), 1320 (s), 1265 (w), 1172 (w), 1111 (w), 1090 (w), 1064 (m), 1010 (m), 968 (vw), 850 (vw), 833 (w), 819 (s), 730 (vw), 711 (vw), 687 (s), 610 (s), 545 (s), 498 (m), 474 (m), 460 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 7.35 (d, J = 8.5 Hz, 2H), 7.56 (d, J = 8.5 Hz, 2H), 7.74 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 122.31, 128.68, 131.70, 136.79, 164.28. MS calcd m/z 232.1, found 231. Anal. calcd for C₇H₆BrNOS: C, 36.22; H, 2.61; N, 6.03; S, 13.82%. Found: C, 36.16; H, 2.64; N, 6.11; S, 13.74%.

4-Methoxyphenyl S-thiocarbamate. Reaction afforded white crystals (93% yield), mp = 128–130 °C (lit.,²⁹ 131 °C). IR (KBr); 3416 (s), 3315 (s), 3294 (s), 3174 (s), 3018 (w), 2970 (s), 2943 (s), 2917 (s), 1656 (vs), 1608 (s), 1594 (s), 1491 (s), 1461 (s), 1441 (w), 1356 (m), 1300 (s), 1289 (s), 1256 (s), 1189 (w), 1174 (m), 1108 (w), 1033 (s), 828 (vs), 801 (m), 741 (vw), 414 (m), 682 (s), 597 (m), 538 (s), 509 (s), 474 (m), 443 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 3.74 (s, 3H), 6.93 (d, J = 8.8 Hz, 2H), 7.33 (d, J = 8.8 Hz, 2H), 7.57 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 55.16, 114.42, 119.56, 136.83, 159.83, 165.93. MS calcd m/z 183.23, found 183. Anal. calcd for C₈H₉NO₂S: C, 52.44; H, 4.95; N, 7.64; S, 17.50%. Found: C, 52.51; H, 5.04; N, 7.57; S, 17.41%.

Naphthalen-2-yl S-thiocarbamate. Reaction afforded white crystals (84% yield), mp = 173–175 °C. IR (KBr); 3414 (s), 3317 (s), 3298 (s), 3172 (m), 3047 (m), 1648 (vs), 1610 (m), 1494 (wv), 1341 (vw), 1315 (s), 1092 (w), 1155 (w), 1132 (w), 1080 (w), 972 (w), 945 (m), 888 (m), 856 (s), 824 (s), 839 (s), 806 (w), 687 (s), 650 (w), 608 (w), 598 (vw), 530 (m), 474 (m), 469 (m), 454 (m), 442 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6) δ ppm; 7.52 (m, 3H), 7.74 (br, s, 2H, NH), 7.91 (m, 3H), 8.06 (s, 1H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6) δ ppm; 126.50, 126.61, 126.92, 127.50, 127.66, 128.08, 131.98, 132.46, 132.96, 134.25, 165.14. MS calcd m/z 203.26, found 203. Anal. calcd for C₁₁H₉NOS: C, 65.00; H, 4.46; N, 6.89; S, 15.78%. Found: C, 64.91; H, 4.34; N, 7.02; S, 15.64%.

Ethyl S-thiocarbamate. Reaction afforded white crystals (91% yield), mp = 105–107 °C (lit.,²⁹ 106–108 °C). IR (KBr); 3365 (s), 3192 (s), 2971 (m), 2932 (m), 1640 (vs), 1439 (m), 1306 (s), 1256 (s), 1112 (m), 1055 (vw), 978 (m), 876 (vw), 842 (s), 713 (s), 680 (m), 571 (w), 433 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6) δ ppm; 1.14 (t, J = 7.5 Hz, 3H), 2.70 (q, J = 7.5 Hz, 2H), 7.41 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 15.86, 23.02, 166.98. MS calcd m/z 105.19, found 105. Anal. calcd for C₃H₇NOS: C, 34.26; H, 6.71; N, 13.32; S, 30.49%. Found: C, 34.25; H, 6.67; N, 13.39; S, 30.41%.

Propyl S-thiocarbamate. Reaction afforded white crystals (89% yield), mp = 92–93 °C (lit.,²⁹ 94 °C). IR (KBr); 3372 (s), 3216 (s), 3184 (s), 2970 (m), 2984 (m), 1641 (vs), 1439 (m), 1310 (s), 1255 (s), 1112 (m), 1057 (vw), 978 (m), 845 (s), 747 (vw), 714 (vs), 679 (s), 579 (m), 433 (m), 420 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6) δ ppm; 0.88 (t, J = 7.5 Hz, 3H), 1.49 (sext, J = 7.0 Hz, 2H), 2.69 (t, J = 7.0 Hz, 2H), 7.41 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 13.82, 24.30, 31.42, 167.80. MS calcd m/z 119.19, found 119. Anal. calcd for C₄H₉NOS: C, 40.31; H, 7.61; N, 11.75; S, 26.90%. Found: C, 40.25; H, 7.64; N, 11.79; S, 26.95%.

1-Butyl S-thiocarbamate. Reaction afforded white crystals (90% yield), mp = 95–97 °C (lit.,²⁹ 96 °C). IR (KBr); 3388 (s), 3290 (s), 3216 (s), 3181 (s), 2956 (s), 2933 (s), 2874 (m), 2861 (m), 1644 (vs), 1320 (m), 1295 (m), 1271 (m), 1225 (m), 1176 (m), 1113 (m), 1052 (vw), 996 (vw), 911 (w), 873 (w), 837 (w), 745 (m), 712 (s), 635 (w), 564 (m), 444 (w), 426 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 0.84 (t, J = 7.5 Hz, 3H), 1.31 (m, 2H), 1.46 (m, 2H), 2.71 (t, J = 7.0 Hz, 2H), 7.41 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 13.43, 21.22, 28.33, 32.26, 166.99. MS calcd m/z 133.21, found 133. Anal. calcd for C₅H₁₁NOS: C, 45.08; H, 8.32; N, 10.51; S, 24.07%. Found: C, 45.02; H, 8.34; N, 10.59; S, 24.05%.

1-Pentyl S-thiocarbamate. Reaction afforded white crystals (92% yield), mp = 92–94 °C (lit.,²⁹ 94 °C). IR (KBr); 3381 (s), 3190 (s), 2956 (s), 2931 (s), 2857 (s), 1643 (vs), 1458 (m), 1302 (s), 1274 (m), 1216 (m), 1113 (m), 893 (w), 874 (w), 846 (m), 736 (m), 708 (s), 679 (m), 562 (m), 464 (m), 427 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 0.86 (t, J = 7.5 Hz, 3H), 1.20 (m, 4H), 1.49 (m, 2H), 2.71 (qun, J = 7.0 Hz, 2H), 7.34 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 13.76, 21.64, 28.62, 29.86, 30.29, 167.01. MS calcd m/z 147.24, found 147. Anal. calcd for C₆H₁₃NOS: C, 48.49; H, 8.90; N, 9.51; S, 21.78%. Found: C, 48.42; H, 8.81; N, 9.58; S, 21.14%.

1-Octyl S-thiocarbamate. Reaction afforded white crystals (90% yield), mp = 94–96 °C (lit.,²⁹ 96 °C). IR (KBr); 3380 (s), 3294 (vw), 3188 (s), 2956 (s), 2928 (s), 2851 (s), 1648 (vs), 1617 (w), 1460 (m), 1298 (s), 1239 (w), 1197 (w), 1165 (w), 1114 (w), 891 (vw), 836 (m), 747 (m), 708 (s), 560 (m), 456 (w), 431 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 0.82 (t, J = 3.5 Hz, 3H), 1.22 (m, 10H), 1.45 (m, 2H), 2.68 (t, J = 5.0 Hz, 2H), 7.40 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 13.85, 22.04, 28.11, 28.50, 28.58, 28.65, 30.18, 31.19, 166.97. MS calcd m/z 189.32, found 189. Anal. calcd for C₉H₁₉NOS: C, 57.10; H, 10.12; N, 7.40; S, 16.94%. Found: C, 57.03; H, 10.13; N, 7.45; S, 16.89%.

2-Butyl S-thiocarbamate. Reaction afforded white crystals (83% yield), mp = 21–23 °C (lit.,²⁹ 22–24 °C). IR (KBr); 3392 (s), 3294 (s), 3221 (s), 3187 (s), 2957 (s), 2933 (s), 2861 (m), 1644 (vs), 1463 (wv), 1410 (wv), 1320 (m), 1295 (m), 1271 (m), 1226 (w), 1200 (wv), 1174 (w), 1113 (m), 1049 (vw), 911 (vw), 876 (w), 835 (w), 745 (m), 712 (s), 564 (m), 445 (w), 427 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 0.54 (t, J = 7.5 Hz, 3H), 0.87 (d, J = 7.5 Hz, 3H), 1.18 (quint, J = 7.5 Hz, 2H), 2.93 (sext, J = 7.5 Hz, 1H), 6.66 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 11.24, 21.31, 29.41, 40.59, 167.05. MS calcd m/z 133.21, found 133. Anal. calcd for C₅H₁₁NOS: C, 45.08; H, 8.32; N, 10.51; S, 24.07%. Found: C, 44.97; H, 8.35; N, 10.62; S, 24.03%.

tert-Butyl S-thiocarbamate. Reaction afforded white crystals (81% yield), mp = 88–90 °C (lit.,²⁹ 90–91 °C). IR (KBr); 3386 (s), 3315 (s), 3216 (s), 3176 (s), 2964 (s), 2925 (m), 2878 (m), 1644 (vs), 1617 (w), 1459 (m), 1376 (w), 1302 (s), 1276 (m), 1222 (m), 1151 (w), 1115 (w), 1057 (vw), 1015 (vw), 999 (vw), 954 (w), 829 (w), 786 (w), 708 (s), 558 (m), 453 (w), 420 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 1.20 (s, 9H), 7.33 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 21.97, 32.38, 166.38. MS calcd m/z 133.21, found 133. Anal. calcd for C₅H₁₁NOS: C, 45.08; H, 8.32; N, 10.51; S, 24.07%. Found: C, 45.02; H, 8.34; N, 10.59; S, 24.05%.

Benzyl S-thiocarbamate. Reaction afforded white crystals (86% yield), mp = 96–98 °C (lit.,²⁹ 98 °C). IR (KBr); 3410 (s), 3317 (s), 3297 (s), 3175 (m), 3055 (w), 3020 (w), 2922 (m), 1647 (vs), 1611 (w), 1492 (m), 1404 (w), 1364 (w), 1315 (s), 1207 (w), 1180 (w), 1105 (w), 1020 (vw), 844 (m), 810 (s), 707 (m), 688 (s), 638 (w), 606 (s), 527 (vs), 274 (w), 463 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 4.01 (s, 2H), 7.27 (m, 5H), 7.56 (s, br, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 32.77, 126.71, 128.28, 128.52, 139.20, 166.57. MS calcd m/z 167.23, found 167. Anal. calcd for C₈H₉NOS: C, 57.46; H, 5.42; N, 8.38; S, 19.17%. Found: C, 57.43; H, 5.43; N, 8.41; S, 19.08%.

1-Phenylurea. Reaction afforded white crystals (90% yield), mp = 145–147 °C (lit.,⁴¹ 147 °C). IR (KBr); 3428 (vs), 3312 (vs), 3038 (m), 1652 (vs), 1616 (vs), 1594 (vs), 1558 (vs), 1500 (m), 1357 (s), 1291 (w), 1257 (m), 1194 (w), 1117 (w), 1075 (vw), 1034 (w), 904 (w), 860 (w), 774 (w), 752 (vs), 697 (vs), 621 (w), 588 (s), 496 (m), 443 (vw), 438 (vw) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 5.81 (s, 2H, NH), 6.86 (t, J = 7.5 Hz, 1H), 7.19 (t, J = 7.5 Hz, 2H), 7.36 (d, J = 7.5 Hz, 2H), 8.48 (s, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 117.64, 120.98, 128.52, 140.46, 155.94. MS calcd m/z 136.15, found 136. Anal. calcd for C₇H₈N₂O: C, 61.75; H, 5.92; N, 20.58%. Found: C, 60.83; H, 5.83; N, 21.04%.

1-(4-Methylphenyl)urea. Reaction afforded white crystals (92% yield), mp = 181–183 °C (lit.,⁴¹ 182–183 °C). IR (KBr); 3428 (vs), 3311 (vs), 3042 (m), 2919 (m), 1652 (vs), 1600 (vs), 1553 (vs), 1408 (m), 1357 (s), 1304 (w), 1280 (w), 1257 (m), 1110 (m), 1024 (m), 931 (vw), 871 (w), 825 (vw), 812 (vs), 779 (s), 708 (vw), 638 (vw), 551 (m), 502 (m), 484 (vw), 416 (vw) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.18 (s, 3H), 5.76 (s, 2H, NH), 6.99 (d, J = 8.5 Hz, 2H), 7.25 (d, J = 8.5 Hz, 2H), 8.37 (s, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 20.22, 117.78, 128.92, 129.70, 137.89, 156.03. MS calcd m/z 150.18, found 150. Anal. calcd for C₈H₁₀N₂O: C, 63.98; H, 6.71; N, 18.65%. Found: C, 63.86; H, 6.75; N, 18.64%.

1-(4-Chlorophenyl)urea. Reaction afforded white crystals (87% yield), mp = 202–204 °C (lit.,⁴¹ 204–205 °C). IR (KBr); 3420 (vs), 3289 (vs), 2874 (w), 1652 (vs), 1614 (vs), 1591 (vs), 1548 (vs), 1492 (m), 1401 (m), 1357 (s), 1296 (w), 1275 (m), 1251 (m), 1112 (vw), 1092 (s), 1014 (m), 870 (s), 820 (vs), 773 (m), 731 (s), 686 (w), 622 (w), 504 (s), 491 (s), 452 (vw) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 5.90 (s, 2H, NH), 7.22 (d, J = 8.0 Hz, 2H), 7.41 (d, J = 8.0 Hz, 2H), 8.65 (s, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 119.16, 124.51, 128.33, 139.43, 155.85. MS calcd m/z 170.02, found 170. Anal. calcd for C₇H₇ClN₂O: C, 49.28; H, 4.14; N, 16.42%. Found: C, 49.21; H, 4.16; N, 16.44%.

1-(3-Bromophenyl)urea. Reaction afforded white crystals (85% yield), mp = 165–167 °C (lit.,⁴¹ 166–168 °C). IR (KBr); 3436 (vs), 3312 (vs), 3210 (vs), 2983 (w), 1670 (vs), 1614 (vs), 1591 (vs), 1526 (s), 1477 (m), 1416 (m), 1345 (s), 1255 (w), 1138 (m), 1069 (m), 1015 (vw), 929 (w), 847 (s), 830 (vs), 786 (m), 768 (vw), 747 (s), 707 (w), 684 (vs), 599 (w), 558 (m), 427 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 6.09 (s, 2H, NH), 7.01–7.20 (m, 3H), 7.79 (d, J = 1.7 Hz, 1H), 9.15 (s, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 116.30, 119.73, 121.53, 123.25, 130.35, 142.44, 155.88. MS calcd m/z 213.97, found 214. Anal. calcd for C₇H₇BrN₂O: C, 39.10; H, 3.28; N, 13.03%. Found: C, 39.01; H, 3.25; N, 13.04%.

1-(4-Methoxyphenyl)urea. Reaction afforded white crystals (90% yield), mp = 164–166 °C (lit.,⁴¹ 165–168 °C). IR (KBr); 3455 (vs), 3338 (vs), 2940 (w), 2838 (w), 1681 (vs), 1650 (vs), 1619 (vs), 1598 (vs), 1466 (s), 1346 (m), 1302 (m), 1248 (s), 1155 (m), 1108 (vw), 1038 (m), 876 (vw), 823 (m), 786 (m), 559 (s), 520 (w) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.06 (s, 3H), 5.70 (s, 2H, NH), 6.78 (d, J = 9 Hz, 2H), 7.27 (d, J = 9 Hz, 2H), 8.29 (s, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 55.02, 113.73, 119.43, 123.08, 133.57, 156.14. MS calcd m/z 166.07, found 166. Anal. calcd for C₈H₁₀N₂O₂: C, 57.82; H, 6.07; N, 16.86%. Found: C, 57.73; H, 6.05; N, 16.93%.

1-(4-(Dimethylamino)phenyl)urea. Reaction afforded white crystals (81% yield), mp = 117–119 °C. IR (KBr); 3432 (vs), 3310 (vs), 2980 (vw), 2882 (m), 1655 (vs), 1603 (vs), 1541 (vs), 1525 (vs), 1350 (s), 1258 (m), 1224 (m), 1188 (w), 1166 (w), 1126 (w), 1061 (m), 1025 (w), 1006 (w), 947 (s), 882 (m), 813 (vs), 772 (w), 751 (w), 683 (vw), 633 (vw), 553 (m), 521 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.78 (s, 6H), 5.60 (s, 2H, NH), 6.63 (d, J = 9 Hz, 2H), 7.17 (d, J = 9 Hz, 2H), 8.11 (s, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 40.82, 113.26, 119.63, 122.77, 145.88, 156.25. MS calcd m/z 179.11, found 179. Anal. calcd for C₉H₁₃N₃O: C, 60.32; H, 7.21; N, 23.45%. Found: C, 60.27; H, 7.25; N, 23.53%.

1-Butylurea. Reaction afforded white crystals (93% yield), mp = 93–95 °C (lit.,⁴¹ 94–96 °C). IR (KBr); 3430 (vs), 3355 (vs), 2960 (vs), 2936 (vs), 2872 (vs), 1649 (vs), 1602 (vs), 1566 (vs), 1478 (m), 1461 (m), 1389 (w), 1362 (s), 1328 (s), 1265 (m), 1158 (s), 1125 (w), 1060 (vw), 996 (vw), 780 (m), 744 (m), 660 (vw), 653 (vs), 434 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 1.45 (t, J = 7.5 Hz, 3H), 1.89 (m, 4H), 3.51 (t, J = 6.2 Hz, 2H), 6.00 (s, 2H, NH), 6.57 (s, 1H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 13.61, 19.44, 32.00, 38.75, 158.84. MS calcd m/z 116.09, found 116. Anal. calcd for C₅H₁₂N₂O: C, 51.70; H, 10.41; N, 24.12%. Found: C, 51.61; H, 10.45; N, 24.04%.

1,1-Dimethylurea. Reaction afforded white crystals (83% yield), mp = 177–179 °C (lit.,⁴¹ 178–183 °C). IR (KBr); 3407 (s), 3204 (s), 2934 (m), 2871 (vw), 1650 (s), 1611 (s), 1513 (s), 1407 (s), 1277 (m), 1180 (w), 1102 (m), 1072 (m), 1027 (m), 876 (vw), 775 (s), 722 (m), 606 (s), 556 (s) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 2.73 (s, 6H), 5.74 (s, 2H, NH). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 35.85, 159.01. MS calcd m/z 88.11, found 88. Anal. calcd for C₃H₈N₂O: C, 40.90; H, 9.15; N, 31.79%. Found: C, 40.83; H, 9.19; N, 31.84%.

1-Benzylurea. Reaction afforded white crystals (86% yield), mp = 142–144 °C (lit.,⁴¹ 143–146 °C). IR (KBr); 3429 (s), 3321 (s), 3031 (m), 2932 (m), 2881 (m), 1652 (s), 1594 (s), 1565 (s), 1468 (m), 1457 (m), 1383 (m), 1328 (v), 1312 (m), 1208 (vw), 1143 (m), 1110 (w), 1026 (w), 912 (vw), 750 (m), 696 (s), 585 (s), 547 (vw), 464 (m) cm⁻¹. ¹H-NMR (250 MHz, 298 K, DMSO-d6), δ ppm; 4.17 (s, 2H), 5.56 (s, 2H, NH), 6.44 (s, 1H, NH), 7.28 (m, 5H). ¹³C-NMR (63 MHz, 298 K, DMSO-d6), δ ppm; 42.75, 126.47, 126.43, 128.13, 140.82, 158.72. MS calcd m/z 150.18, found 150. Anal. calcd for C₈H₁₀N₂O: C, 43.98; H, 6.71; N, 18.65%. Found: C, 43.83; H, 6.63; N, 18.74%.

Conclusion

In conclusion, we have developed a novel and highly efficient method for the synthesis of various primary carbamates, S-thiocarbamates and ureas by the treatment of structurally varied alcohols, phenols, thiols and amines with potassium cyanate in the presence of DBSA, as an efficient, eco-friendly and versatile reagent. The solvent-free conditions, mildness of the conversion, simple experimental procedure, clear reaction profiles, high yields and purity, and short reaction times are the noteworthy advantages of the protocol. Furthermore, this method does not have disadvantages such as involvement of toxic solvents and reagents,^4–12,22 expensive starting materials,^11–14 formation of any undesirable side products, and epimerization. Further studies are in progress.^22,23

Acknowledgements

Authors gratefully acknowledge the financial support of this work by the research council of Shiraz University.

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Footnote

† Electronic supplementary information (ESI) available: Copies of FT-IR, ¹H- and ¹³C-NMR, MS spectra for all compounds. See DOI: 10.1039/c5ra14528g

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