Isothioureas mercaptans

The flotation results of pyrite using various isothioureas at different pH conditions are shown in Fig. 1.6. It is shown in Fig. 1.6 that isothiourea has no collecting capability in acid medium because isothiourea does not undergo hydrolysis. The flotation performance of isothiourea is better than those of other two reagents in alkaline medium because isothiourea is converted to mercaptan. Based on these results, functional mechanism of isothiourea is that the hydrolysis product of isothiourea (mercaptan) and the oxidation product of mercaptan (organic bisulfide) are effective collectors. Therefore, the flotation performance of isothiourea depends... 

The thermal dissociation of S-alkyl-N,N -diphenyhsothioureas into mercaptans and diphenylcarbodiimide was already discovered during the last century. " Schlack and Keil utilized this reaction to synthesize several dicycloalkyl andbis-carbodiimides 29 by heating the isothioureas 28 at 125-240 °C under vacuum (yields 40-90 %). 

Oxidations by chlorine are limited to only few types of compounds. In organic solvents and pyridine [681] or hexamethylphosphoramide (HMPA) [682] as cosolvents, primary alcohols are oxidized to aldehydes and secondary alcohols to ketones [681, 682]. Secondary alcohols are oxidized in preference to primary alcohols [681]. Many oxidations with chlorine are carried out in aqueous media and involve sulfur-containing compounds. Mercaptans [683], alkyl thiolcarboxylates [683], thiocyanates [684], isothioureas [684], disulfides [655], and sulfinic acids [656] are transformed into sulfonyl chlorides. The chlorination of dimethyl disulfide in acetic anhydride yields methanesulfinyl chloride [657]. 

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... 

Methylindole, 22, 94 Methyl isothiocyanate, 21, 81, 83 Methyl isothiourea, reaction of sulfate with hydrazine sulfate, 26, 9 Methyl lactate, 26, 6 6-Methyllepidine, 26, 47 8-MethyUepidine, 26, 47 a-Methyl-d-mannoside, 22, 86 Methyl mercaptan, 26, 9 N-Methyl- (3 methoxy-4-hydroxy-phenyl)-alanine, 22, 91 2-Methyl-6-methoxyqumohne, 26, 47 Methyl myristate, 20, 67 a-Methylnaphthalene, 26, 93 Methyb -octylamine, 25, 19 Methyl palmitate, 20, 67 Methylphenyldiketoke, 23,1 /3-(2-MEIH LPHENYL)-JiTUYLAMlNE, 23, 72... 

Alkyl isothiourea is easily broken down into mercaptan and cyanamide. Therefore, the reverse reaction of decomposition reaction can be used to produce alkyl isothiourea. The reverse reaction of decomposition reaction is as follows ... 

The explanation for the effect of pH on the flotation performance of isothiourea lies in that isothiourea is converted rapidly to mercaptan. The hydrolytic process of isothiourea is as follows ... 

Prepared from /7-hydrorQrmetbyl sulfide and thionyl ddmide (403) essentially by the method of Kimer (462). j9-hydroxymethyl sulfide is prepared from methyl isothiourea sulfate through methyl mercaptan and sodium methyl sulfide and reaction of the latter with ethylene ehlorohydtin by the method of Windus and Shildneck (868). Methyl mercaptan is available commercially. 

Ethylene glycol bis- (y-aminopropyl) ether added dropwise to er butyl isothiocyanate in ethanol, and stirred 1 hr. after heat evolution has subsided, the ethanol removed by distillation with dropwise replacement by water, dimethyl sulfate added to the resulting aq. suspension of the thiourea, refluxed 30 min., the soln. obtained added dropwise at 0-10° to excess Na-carbonate soln., stirred 1 hr., the resulting crude isothiourea heated 0.5 hr. at 175°, then refluxed 1 hr., and the mercaptan elimination completed by refluxing 0.5 hr. at 200°/12 mm 3,3 -bis-( ert-butylcarbodiimido) ethylene glycol dipropyl ether. Y 85%. F. e. and methods s. P. Schlack and G. Keil, A. 661, 164 (1963). 

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