Pyridine reaction with thiourea

The preparation of mercaptopyrazines (1) by the reaction of halogenopyrazines with sodium (or potassium) hydrogen sulfide or sodium polysulfide in various solvents (780, 790, 799, 805, 809, 821, 858, 890, 892, 993, 1006-1011), by reaction with phosphorus pentasulfide in pyridine (1013), and by reaction with thiourea in acid (905) and in alcohol followed by alkali (535) has been described in Section V.5G. 

Cellulose reacts with isocyanates in anhydrous pyridine or with urea and substituted ureas at relatively high temperature to yield carbamates. The optimum carbamation reaction of microcrystalline cellulose with urea in a dry solid mixture has been studied [51]. In addition, a preferentially C6-modified cellulose carbamate derivative has been obtained [52]. Heating of cellulose with thiourea at 180°C yielded cellulose thiocarbamate [53]. Heat treatment of cellulose isocyanate products has been utilized for the production of urethanes [54]. When ceUuIose was treated with phenylisocyanate at 100 C in DMF in the presence of dibutyltin dilaurate and triethylenediamine, celiuiose bisphenylcarbamate was formed [55]. Treatment of cellulose with urea at temperatures at or above the latter s melting point (where urea decomposes into isocyanic acid and ammonia) has been employed for the production of cellulose carbamates fibers [56]. The advantages and disadvantages of using urea as an intermediate for production of fiber have been discussed [57]. 

Dehuri and Nayak (83JIC970) reported that 3,4,5,6,7,8-hexahydro-l,3-diazocine-2-thione (213), obtained from 1,5-dibromopentane and thiourea in boiling ethanol, reacts with chloroacetic acid or its ethyl ester followed by basification to give 5//-6,7,8,9-tetrahydrothiazolo[3,2-a]-[ 1,3]diazocin-3(2//)-one (214). The reaction of 213 with ethyl chloroacetate was not smooth and the yield was low. The thione 213, on reaction with ethyl chloroacetate and aromatic aldehydes in the presence of pyridine and piperidine, furnishes the arylidene product 215 which is also obtained from 214 and aromatic aldehydes. No spectral data are cited to confirm the thiazolidinone structures 214 and 215 (Scheme 50). 

Pseudothiohydantoine, as acyclic intermediate, in reaction of o-halogeno acids or esters with thiourea, 232. See also 2-Amino-4-hydroxythiazole Pyridazines (4,7-dioxo-4,5,6,7-tetrahydro-thiazolo[4,5d]), preparation of, 206 Pyridine, electronic structure, 36, 39, 46 ultraviolet absorption, 47 thiazolylation of, 373 2-(4-Pyridyl)-4-carboxyethylthiazoie, from thioisonicotinamide and ethyl bromopyruvate, 198... 

Analogous methods lead to benzimidazolethiones when o-phenylene-diamine.s arc treated with carbon disulfide, ihiophosgene, l.l -thiocarbonyldi-imidazolc, thioureas, thiocyanates or potassium ethyl xanthate [123, 126-129]. The reactions with carbon disulfide take place in basic media, e.g. with KOH or pyridine. Again, microwave irradiation offers advantages 1123]. 

Methyl-2-oxo-l, 2-dihydropyrazine with phosphorus pentasulfide in pyridine at reflux was converted into l-methyl-2-thio-l,2-dihydropyrazine (18) (821,1100), and 3-chloropyrazine 1-oxide with sodium hydrogen sulflde in ethanol at room temperature gave 3-mercaptopyrazine 1-oxide (19) (1035). Whereas 3-chloro-2,5-dimethyipyrazine 1-oxide reacted slowly with thiourea in ethanol, and the use of water in place of ethanol caused some increase in reaction rate, the reaction in 2A sulfuric acid at reflux for 30 minutes gave 3-mercapto-2,5-dimethylpyrazine 1-oxide (85%), and 3-mercapto-2-methylpyrazine 1-oxide was prepared similarly (905). 

The cyclization of o-ureidobenzoic esters to quinazoline-2,4-diones and 4-one-2-thiones, respectively, in aqueous alkali proceeded equally well with the N-hydroxy urea (X = O) and thiourea (X = S) esters 28. If the reagents were altered to triethylamine in pyridine the 2,l-benzisoxazol-3-ones were formed. Ethyl o-hydroxyaminobenzoate reacted with two molecular equivalents of methylisocyanate in ethanolic alkali and gave 3-methyl-l-methyl-aminocarbonyloxyquinazoline-2,4-dione. When three molecular equivalents were used the tricyclic quinazoline 29 was obtained. A similar reaction with methylisothiocyanate did not behave in the same way, and 3-methylquina-zolin-4-one-2-thione was formed. It was shown that the intermediate 1-hydroxy derivative (30) gave 3-methylquinazolin-4-one-2-thione, i.e., loss of the 1-oxygen atom, on further treatment with methylisothiocyanate in the presence of triethylamine. The preparation of quinazoline-2,4-diones by... 

Considering that the chemical reactivity of carboxylic acids is similar to that of carbonic acids, as is observed in amide and ester formation, we have attempted the substitution of carbon dioxide for carboxylic acids in the coupling reaction with amines by using phosphites in pyridine or imidazole, and found that ureas are in fact produced in good yields (Eq. (4))6. Similarly, carbon disulfide reacts with amines to yield the corresponding thioureas (Eq. (5)). 

Chloro substituents both in the pyrimidine and the pyridine part of pyrido[3,2-d]pyrimidines 8 have been exchanged for sulfanyl groups by reaction with alkyl-77,442 as well as aryl-458 thiolates. For the introduction of sulfanyl groups, thiourea is the reagent of choice.77,134... 

Thiadiazines (229) are rearranged into triazines (230) and (231) on treatment with sodium hydroxide and amines respectively (Scheme 71) <91NKK1655, 92NKK1450> while the 1,3,5-thi-adiazinetrithiones (232), which were prepared by the reaction of thioureas with ethyl chloroformate in the presence of pyridine, react with anilines to give the 1,3,5-triazines (233) or (234) (Scheme 72) <88PIA53>. 

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