Thiourea mercaptans

Regarding the substituent effect on reactivity of groups in positions 4 and 5 there is little information in the literature. The reactivity of halogen in position 5 seems to be increased when an amino group is present in position 2. Substitution products are easily obtained using neutral nucleophiles such as thiourea, thiophenols, and mercaptans (52-59). 

If tertiary chlorine atoms are indeed critical to heat resistance, then reactions that consume them should improve polymer stabiUty. This is indeed the case. Post-reaction of polychloroprene with dodecyl mercaptan (111), use of higher levels of ethylene thiourea for curing (112), and inclusion of reactive thiols such as mercaptobenzimidazole in cure systems (113) all improve heat resistance. This latter technique is especially effective in improving the heat resistance of mercaptan modified polychloroprene. 

As yet, a number of experiments have failed to convert ureas 205 such as N-phenylurea or imidazolin-2-one by silylation amination with excess amines R3NHR4 such as benzylamine or morpholine and excess HMDS 2 as well as equivalent amounts of NH4X (for X=C1, I) via the silylated intermediates 206 and 207 in one reaction step at 110-150°C into their corresponding guanidines 208 with formation of NH3 and HMDSO 7 [35] (Scheme 4.13). This failure is possibly due to the steric repulsion of the two neighbouring bulky trimethylsilyl groups in the assumed activated intermediate 207, which prevents the formation of 207 in the equilibrium with 206. Thus the two step Rathke-method, which demands the prior S-alkylation of 2-thioureas followed by amination with liberation of alkyl-mercaptans, will remain one of the standard syntheses of guanidines [21, 35a,b,c]. 

Further routes of cyclizations have been studied in parallel in the case of cis- and rra/J5-2-hydroxymethyl-l-cyclohexylamine (106) (880PP73). The preparation of thiourea or urea adducts 107 and 108 with phenyl isothiocyanate or phenyl isocyanate proceeds smoothly. The reaction of 107 with methyl iodide and subsequent alkali treatment, by elimination of methyl mercaptan, resulted in the iminooxazine 109 in high yields. The ring closures of both cis and trans thiourea adducts to 1,3-oxazines proceed with retention. Cyclodesulfuration of the adduct 107 by mercury(II) oxide or N,N -dicyclohexylcarbodiimide resulted in the iminooxazine 109, but the yield was low and the purification of the product was cumbersome. The ring closure of 108 with thionyl chloride led to the iminooxazine 109 in only moderate yield. 

Furfuryl mercaptan is prepared from furfuryl alcohol, thiourea, and hydrogen chloride. The resulting ri -furfurylisothiouronium chloride is cleaved with sodium hydroxide to give furfuryl mercaptan. 

A mixture of 125 g. (0.5 mole) of w-dodecyl bromide (Note 1), 38 g. (0.5 mole) of thiourea, and 250 cc. of 95 per cent ethyl alcohol is refluxed on a steam cone for three hours (Notes 2, 3, and 4). A solution of 30 g. (0.75 mole) of sodium hydroxide in 300 cc. of water is added, and the mixture is refluxed for two hours. During this period the mercaptan separates as a pink to red oil. The layers are separated, and the aqueous layer is acidified with dilute sulfuric acid (7 cc. of concentrated acid to 50 cc. of water) and then extracted with one 75-cc. portion of benzene (Note 5). The extract is added to the crude mercaptan layer, and the whole is washed twice with 200-cc. portions of water and... 

In addition to the compounds described in the following paragraphs, see also Hydrogen Sulfide Mercaptan Sodium Thiosulfate Sulfuric Acid Sulfurous Acid Thiocyanic Acid Thiocthcrs Thiophene and Thiourea. 

Furfuryl mercaptan cannot be prepared according to the classical method using furfuryl chloride and potassium sulfide.2 It has been prepared by reduction of 2-furfuryl disulfide, obtained from furfural and ammonium hydrosulfide.3 The mercaptan has also been obtained in 33% yield 2 by the reaction of furfuryl chloride with thiourea and subsequent decomposition of the intermediate S-2-furfurylisothiourea according to the general method described in Organic Syntheses.4 In the present method, which has been published previously, the use of the very unstable and difficultly available furfuryl halides is avoided.6... 

The thiols are the sulphur analogues of the alcohols and were formerly called the mercaptans. Although they may be prepared by the interaction of an alkyl halide and sodium hydrosulphide in ethanolic solution, a better method involves the interaction of an alkyl bromide and thiourea to form an S-alkylisothiouronium salt, followed by hydrolysis of the latter with sodium hydroxide solution. 

In the investigation of the cleavage of S-substituted thioureas (24), the increase in the anodic wave of the mercaptans formed can be followed. In this base-catalysed reaction, the reactivities of hydroxyl and carbonate ions are considerably greater than those of the other bases investigated (borate, bicarbonate, ammonia, phosphate and monohydrogen phosphate). There is some analogy with base-catalysed ester hydrolysis. 

A mixture of 51 g. (0.5 mole) of n-hexyl alcohol, 38 g. (0.5 mole) of thiourea, and 256 g. (1.5 moles) of 48% hydrobromic acid is stirred and heated to reflux for 9 hours. A solution of 60 g. (1.5 moles) of sodium hydroxide in 600 ml. of water is added, and the resulting mixture is heated under reflux for 2 hours, without stirring and with a stream of nitrogen passing over the surface of the liquid. The layers are separated, and the aqueous layer is acidified and extracted with ether. The combined ethereal extracts are dried over anhydrous calcium sulfate and distilled through a 12-in. packed column. n-Hexyl mercaptan is obtained in 71% yield. It boils at 149-152° at atmospheric pressure. 

The following mercaptans are prepared by the same procedure in the yields indicated isobutyl, 56% n-octyl, 73% n-dodecyl, 77% cetyl, 64% /J-phenylethyl, 70% sec-butyl, 64% hexamethylene, 63% and decamethylene, 48%. Double the above molar amounts of hydrobromic acid and thiourea are used in the preparation of hexamethylene and decamethylene mercaptan. 

As to the nucleophiles that can be applied in the nucleophilic reactions, ammonia and amines, water and alcohols, and mercaptans have been mentioned already. Sulfide and thiourea have been used only with the achiral ferrocenylmethylium ion [97]. To obtain chiral derivatives of 1-ferrocenyl-ethylmercaptan, substitution of the acetate with potassium thioacetate in acetic acid, followed by reduction with LiAlH4, was found appropriate [98, 99]. Reaction of (R)-l-ferrocenylethanol with NaH and... 

Sodium sulfhydride (NaSH) is a much better reagent for the formation of thiols (mercaptans) from alkyl halides than H2S and is used much more often. It is easily prepared by bubbling H2S into an alkaline solution, but hydrosulfide on a supported polymer resin has also been used. " The reaction is most useful for primary halides. Secondary substrates give much lower yields, and the reaction fails completely for tertiary halides because elimination predominates. Sulfuric and sulfonic esters can be used instead of halides. Thioethers (RSR) are often side products. The conversion can also be accomplished under neutral conditions by treatment of a primary halide with F and a tin sulfide, such as PhsSnSSnPhs. An indirect method for the preparation of a thiol is the reaction of an alkyl halide with thiourea to give an isothiuronium salt (119), and subsequent treatment with alkali or a... 

The approach works equally well with thio reagents other than mercaptans, e. g., thioacetic acid [37], thiourea [51] or 0,0-dialkylphosphorodithioic acid derivatives [52], to yield the corresponding derivatives with an anomeric sulfur in high yields and stereoselectivity. 

MERCAPTANS 1 -Acetyl-2-thiourea. METHANESULFONATE ESTERS Meth-anesulfonyl chloride. 

Preparation of mercaptans (thiols). An alkyl halide, for example lauryl bromide, reacts with thiourea to give the isothiourea hydrobromide, which on alkaline hydrolysis affords the mercaptan. In the preparation of lauryl mercaptan the... 

A number of chemical treatments have been suggested to reduce the photo-yellowing of bleached and whitened wool. Tetrakishydroxymethyl phosphonium chloride, thiourea (alone or as a formaldehyde condensate) and some mercaptans and reducing agents [20,21 ] and the reaction of wool with sulfamic acid [22] have been shown to offer some protection against photo-yellowing, particularly on wet wool. 

M-Dodecyl mercaptan has been prepared by the action of alkali on the salts of 5- -dodecyl thiourea and by reduction of di- -dodecyl disulfide. ... 

---