Thiourea, reaction with benzyl chloride

Mix 63 g benzyl chloride, 38 g thiourea, 3 drops concentrated NH OH solution, and 250 ml [95% (v/v)] ethanol into a 2L roimd bottom fiask fitted with a double-surface reflux condenser. Reflux the reaction mixture for 3 hours and allow it to cool. 

Add in turn benzyl chloride (8 3 g., 8 o ml.) and powdered thiourea (5 gm.) to 10 ml. of 95% ethanol in a 100 ml. flask fitted with a reflux condenser. Warm the mixture on the water-bath with gentle shaking until the reaction occurs and the effervescence subsides then boil the mixture under reflux for 30 minutes. Cool the clear solution in ice-water, filter off the crystalline deposit of the benzylthiouronium chloride at the pump, wash it with ice-cold ethyl acetate, and dry in a desiccator. Yield, 11-12 g., m.p. 170-174°. The white product is sufficiently pure for use as a reagent. It is very soluble in cold water and ethanol, but can be recrystallised by adding ethanol dropwise to a boiling suspension in ethyl acetate or acetone until a clear solution is just obtained, and then rapidly cooling. 

Method 2. Place a mixture of 126-5 g. of benzyl chloride, 76 g. of thiourea and loO ml. of rectified spirit in a 500 ml. round-bottomed flask fitted with a reflux condenser. Warm on a water bath. A sudden exothermic reaction soon occurs and aU the thiourea passes into solution. Reflux the resulting yellow solution for 30 minutes and then cool in ice. Filter off the white crystals and dry in the air upon filter paper. Concentrate the filtrate to half its original volume and thus obtain a further small crop of crystals. The yield of crude hydrochloric acid as in Method 1 the m.p. is raised to 150°, although on some occasions the form, m.p. 175°, separates. 

A reaction flask charged with A,A -l,4-phenylene-bis-thiourea (230mg) was dissolved in a mixed solution of 4 ml apiece NMP and ethanol and then treated with benzyl chloride (270 mg) and refluxed for 30 minutes. The solution was cooled, treated with a solution of 10 ml water containing NaOH (80 mg), and then extracted with 40 ml of diethyl ether. The extract was dried with MgS04, filtered, concentrated, and 400 mg of product were isolated. 

In the uncondensed imidazoles the standard method reacts an a-aminocarbonyl compound with a thiocyanate (see Section 4.1 and Table 4.1.1). If a 2-alkylthioimidazole is required directly, one can combine an N-alkyT or A -arylcarbonimidodithioate in refluxing acetic acid with the aminocarbonyl substrate (see Section 4.1 and Scheme 4.1.3). Alternatively, reaction between thiourea and a two-carbon synthon (ot-hydroxy-, a-halogeno-, a-dicarbonyl) leads to imidazoline-2-thiones (see Section 4.3). In sulfuric acid, 3-butynylthiourea cyclizes to 4,5-dimethylimidazolin-2-thione (see Section 2.2.1). 1-Substituted 2-methylthioimidazoles can be made, albeit in rather poor yields, from appropriately substituted 2-azabutadienes (see Section 3.2 and Scheme 3.2.3), and 2-arylthioimidazoles are available in moderate yields from benzyl isocyanides and arylsulfenyl chlorides (see Section 4.2 and Scheme 4.2.12). Ring transformations of 5-amino-2-alkylaminothiazoles and 2-acylamino-5-aminothiazoles may have occasional applications (see Section 6.1.2.7). The ease with which a thiol group or imidazole or benzimidazole can be alkylated, in comparison with the annular nitrogens, usually makes it more convenient to prepare alkylthioimidazoles from the thiols (or thiones). 

Mercapto pyrimidines 82 were synthesized from acetoacetanilide, dihydroxybenzaldehyde, and thiourea, which were readily alkylated with benzyl chloride to afford 2-benzylthio derivatives 83 (Scheme 32). 83 when reacted with different amines in acetic acid furnished 2-amino derivatives 84 (R = Ar), whereas upon reaction with hydrazine hydrate 83 afforded 2-hydrazinyl derivative 84 (R = NH2), which with different aldehydes gave hydrazones 85 (R = 2-furyl, 2-thienyl). Arylidene thiazolidinone 86 was obtained from 84 with carbon disulfide, monochloroacetic acid, and aryl aldehydes, while 84 with ethyl acetoacetate and different aromatic aldehydes provided pyrazoles 87 (Scheme 32) (10MI9). Such tetrasubstituted pyrimidines act as cyclin-dependent kinase (CDK2) inhibitors. 

Recently copper(i) salts including thiolates have been studied as nucleophiles. Copper(i)butanethiolate and copper(i)cyanide in DMF did not react with t-butyl chloride or benzyl chloride, but halogenoaromatic compounds react under similar conditions. When the reactions were repeated in the presence of thiourea or quinoline, the expected products, di-t-butyl sulphide, valeronitrile and phenylacetonitrile, were obtained. The thiourea or quinoline probably act as ligands and bind strongly to the copper, forming the ion (CuL4)+, leaving the counterion (e.g. BuS from CuSBu) available for normal nucleophilic attack . 

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