- Isocyanates From Primary Amines and Carbon Dioxide: 'Dehydration' of Carbamate Anions
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Carbamate anions, derived from primary amines CO2 and an added base (e.g.NEt3), undergo rapid reaction with electrophilic 'dehydrating agents' (e.g.POCl3, P4O10) to give the corresponding isocyanates in excellent yields.
- Waldman, Thomas E.,McGhee, William D.
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p. 957 - 958
(2007/10/02)
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- Preparation of trans cyclohexane 1,4 diisocyanate
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A process is disclosed for selectively making trans-cyclohexane-1,4-diisocyanate, trans-cyclohexane-1,4-diamine, a trans-cyclohexane-1,4-diurethane, a trans-cyclohexane-1,4-diurea and trans-cyclohexane-1,4-disulphonyl urea by reacting ammonia with a mixture of cis and trans-cyclohexane-1,4-dicarboxylic acid, a lower alkyl ester, a glycol ester, an oligomeric ester or a polyester to make a solid trans-dicarboxylic acid diamide in a first step. The diamide is chlorinated to form cyclohexane-1,4-dicarboxylic acid-bis-N-chloramide. The latter compound is then converted into a (a) trans-cyclohexane-1,4-diamine with an alkali metal hydroxide or alkaline earth metal hydroxide; or into a (b) a trans-cyclohexane-1,4-diurethane by reaction with an alcohol or glycol in a reaction mixture containing an alkali metal hydroxide or alkaline earth metal hydroxide; or into (c) a trans-cyclohexane-1,4-diurea by reaction with a primary or secondary amine in a reaction mixture containing an alkali metal hydroxide or alkaline earth metal hydroxide; or into a (d) trans-cyclohexane-1,4-sulphonyl urea by reaction with a primary sulphonamide in a reaction mixture containing an alkali metal hydroxide and dimethyl formamide and water. The diurea prepared in (c) may be converted into trans-cyclohexane-1,4-diisocyanate with gaseous hydrogen chloride in an inert solvent. The diurethane prepared in (b) and the disulphonyl urea prepared in (d) may be thermally decomposed into trans-cyclohexane-1,4-diisocyanate.
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- Process for the preparation of organic mono- and polyisocyanates
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A process for the preparation of organic mono- and polyisocyanates is described, in which a hydrogen chloride adduct of a trisubstituted urea is thermally decomposed to form the isocyanate. The hydrogen chloride adduct at minimum contains the stoichiometric amount of HCl, and at maximum a 10 mole-% excess. The process is carried out in a closed system at a temperature between about 80° and 180° C.; the reaction is effected either in a melt or in the presence of an inert organic solvent.
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