Isothiocyanates, addition hydrolysis

A simple, general route to dithioesters (168) is by the addition of Grignard reagents to phenyl isothiocyanate and hydrolysis of the intermediate imine (167)... 

Several related derivatives have also been utilized in this type of synthesis. Imino-chloromethanesulfenyl chlorides (184), prepared by the controlled addition of chlorine to isothiocyanates, react with amidines (161) to give 1,2,4-thiadiazolines (185) (71T4117). Chlorocarbonylsulfenyl chloride (186), prepared by the hydrolysis of trichloromethanesulfenyl chloride with sulfuric acid, reacted with ureas, thioureas and guanidines to give 1,2,4-thiadiazolidine derivatives (187) <70AG(E)54, 73CB3391). 

Related to this process is the hydrolysis of isocyanates or isothiocyanates" where addition of water to the carbon-nitrogen double bond would give an N-substituted carbamic acid (3). Such compounds are unstable and break down to carbon dioxide (or COS in the case of isothiocyanates) and the amine ... 

TRITC is relatively insoluble in water, but it can be dissolved in DMF or DMSO as a concentrated stock solution prior to its addition to an aqueous reaction mixture. The isothiocyanate group is reasonably stable in aqueous solution for short periods, but will degrade by hydrolysis. TRITC also is more stable to photobleaching than FITC (Section 1, this chapter), and its absorption and emission spectra are less sensitive to environmental conditions, such as plT. It is best, however, to use only fresh reagent for modification purposes. Storage should be done under desiccated conditions, protected from light, and at -20°C. 

When 176 is treated with hydrochloric acid it gives the intermediate acyclic structure 265, which decomposes to sulfonyl isothiocyanates, isothiocyanates, and chlorformamidines. Solvolysis of 155 with ethanol, followed by addition of hydrogen bromide, leads to 266. Base hydrolysis of 156 leads to the zwitterionic structure 267. ... 

Addition of isocyanates and isothiocyanates, followed by hydrolysis, yields amides, thioamides,274-277 or ureides of j8-ketoacids 82 and 83 are examples of typical intermediates in this reaction. 

Despite the chemical diversity of the several hundred structures representing herbicidal activity, most reactions of herbicides fall within only a limited number of mechanistic types oxidation, reduction, nucleophilic displacements (such as hydrolysis), eliminations, and additions. "Herbicides", after all, are more-or-less ordinary chemicals, and their principal transformations in the environment are fundamentally no different from those in laboratory glassware. Figure 2 illustrates three typical examples which have received their share of classical laboratory study—the alkaline hydrolysis of a carboxylic ester (in this case, an ester of 2,4-dichlorophenoxyacetic acid, IX), the cycloaddition of an alcohol to an olefin (as in the acetylene, VI), and the 3-elimination of a dithiocarbamate which provides the usual synthetic route to an isothiocyanate (conversion of an N.N-dimethylcarbamic acid salt, XI, to methyl isothiocyanate). Allow the starting materials herbicidal action (which they have), give them names such as "2,4-D ester" or "pronamide" or "Vapam", and let soil form the walls of an outdoor reaction kettle the reactions and products remain the same. 

Amidines with a more complicated substitution pattern have been prepared from amidines by alkylation—either at nitrogen or at nitrogen substituents. - Variations at these positions have been achieved by heteroarylation, acylation,vinylation or carboxylation with phosgene, thio-phosgene, isocyanide dichlorides or isothiocyanates. Some interesting amidines, e.g. (347)-(3S2) (Scheme 59), have been prepared in this manner. The amidine skeleton can also be varied by halogen-ation, - hydrolysis, isomerization or catalytic hydrogenation or other addition reactions if there are C=—C double bonds present as in (353 equation 173) for example. ... 

But the 1 1 adduct (XIII) is easily formed by slowly dropping phenyl isocyanate into equimolar amounts of Bu3PbNEt2 and petroleum ether. Hydrolysis gives the W-phenyl-W -diethylurea. Cyclohexylisocyanate reacts the same way. From ethyl isothiocyanate oil the adduct (XIV) seems to be formed, but the possibility of an addition to the C==S group is not excluded. In any case triethylthiourea is slowly formed with water. Dicyclohexyl carbodiimide reacts to give W-plumbylguanidine (XV), in which the... 

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