Isothiocyanates dithiocarbamic acids

Salts of dithiocarbamic acid can be prepared by the addition of primary or secondary amines to carbon disulfide. This reaction is similar to 16-9. Hydrogen sulfide can be eliminated from the product, directly or indirectly, to give isothiocyanates (RNCS). Isothiocyanates can be obtained directly by the reaction of primary amines and CS2 in pyridine in the presence of DCC. ° In the presence of diphenyl phosphite and pyridine, primary amines add to CO2 and to CS2 to give, respectively, symmetrically substituted ureas and thioureas ... 

Methyl isocyanate, see Carbaryl, Propoxur Methyl isothiocyanate, see Dazomet Methyl mercaptan, see EPTC. Phorate Methyl(methylaminomethyl)dithiocarbamic acid, see Dazomet... 

Soil. Soil metabolites include formaldehyde, hydrogen sulfide, methylamine, and methyl(methylaminomethyl)dithiocarbamic acid (Hartley and Kidd, 1987), the latter decomposing to methyl isothiocyanate (Ashton and Monaco, 1991 Hartley and Kidd, 1987 Cremlyn, 1991). The rate of decomposition is dependent upon the soil type, temperature, and humidity (Cremlyn, 1991). 

This compound dissociates in solution to yield the starting materials, dithiocarbamic acid and ethoxycarbonyl isothiocyanate <1998EJI1025>. 

Dithiocarbamic acids 557, generated in situ from aliphatic amines and carbon disulfide, react with carbodiimides to give isothiocyanates 558 in 70-99 % yield. ... 

Treatment of 3-amino-6-methoxypyridine or the corresponding thiourea 471 with thiophosgene gives the l,3-thiazetidine-2-thione 472. 1,3-Thiazetidine-2-thiones are possible intermediates in the reaction of carbon disulfide or isothiocyanates with isothioureas,in the reaction of carbon disulfide with imines, " and in the reaction of salts of dithiocarbamic acids with a,/3-unsaturated acid chlorides. 4-Imino-l,3-thiazetidine-2-thione is suggested as an intermediate in reactions of isothiocyanic acid (HNCS). ... 

Even though the most widely used preparation is still the reaction of alkali isothiocyanates or alkyl and aryl isothiocyanates with a-amino carboxylic acid derivatives, the reaction of dithiocarbamic acid esters (CCX) with a-amino carboxylic acids (CCXI) has certain advantages especially in the synthesis of heterocyclically substituted imidazolidin-4-one-2-thiones (221). 

These products can also be obtained from the esters of dithiocarbamic acid and sodium azide 21S). The two reagents are dissolved in a suitable solvent, usually a water-ethanol mixture, and heated until no more alkane thiol is split off. The thione is isolated by acidifying the sodium salt. This method of preparation avoids the use of the difficult to prepare isothiocyanates. 

It appears quite probable that this reaction occurs by the same mechanism as the reaction of nitrous acid with thiosemicarbazides and of sodium azide with isothiocyanates. The primary reaction product is a thiocarbamoyl azide (CCXIII) to which, however, the cyclic structure of a 5-amino-l,2,3,4-thiatriazole (CCXIV) is attributed. In alkaline medium these compounds rearrange to the corresponding 1 -substituted-Zla-tetrazoline-5-thiones (CCXII) 236, 237). A survey of these compounds, prepared from the dithiocarbamic acid esters, is given in Table 33. 

Isothiocyanates. Primary amines are converted into isothiocyanates by combining with carbon disulfide and decomposing the dithiocarbamic acid salts with TsCl. ... 

Aromatic amines are too weak to undergo the above reactions they do add to carbon disulfide but the resulting dithiocarbamic acids cannot form salts the resulting unstable free acids decompose at once with evolution of hydrogen sulfide and formation of isothiocyanates which add the excess of amine and thus give thioureas as final products 93,94 a small amount of sulfur catalyses the formation of the thioureas.95 Treatment of salts of the dithiocarbamic acids obtained in this way with chloroformic esters in chloroform at 0° leads to loss of COS and alcohol and formation of isothiocyanates in high yield.96... 

Ethylene-bis-dithiocarbamic acid (nabam) is a fungicide. Through bioactivation it gives birth to an alkylating di-isothiocyanate, able to block the reactive thiol functions of the parasitic fungus. Af-Methylation of nabam inactivates the compound because it prevents its transformation into diisothiocyanate (Fig. 19.15). 

Without additional reagents Isothiocyanates from dithiocarbamic acid esters... 

Iodine can be used to oxidise the dithiocarbamic acids to an isothiocyanate and sulphur the latter is insoluble and therefore detectable by the turbidity it produces (equations 43 and 44) °. Alternatively the dithiocarbamic acids can be oxidised with iron(m) chloride or mercury(ii) chloride, as in equation (45), and the hydrogen sulphide easily detected . 

The reaction of isothiocyanates with cysteine gives (depending on pH) two types of primary products. In weakly acidic solutions (pH 5-6), isothiocyanate reacts exclusively with the thiol group of cysteine, producing N-substituted esters of dithiocarbamic acids and heterocyclic products. The same products are formed from... 

In a weakly alkaline solution, isothiocyanate reacts with the a-amino group of cysteine (Figure 2.64). The reaction of isothiocyanates with cystine leads to the cleavage of disulfide bond (-S-S-) with the formation of cysteine sulfenic acid and a dithiocarbamic acid ester. Dehydration of this ester yields 5-amino-l,3-thiazine-4-one-3-thione derivative and elimination of hydrogen sulfide produces a cyclic 2-thiazoline-4-carboxylic acid derivative (Figure 2.65). Reaction of cystine with thiocyanates (R-S-C=N), formed by spontaneous isomerisation of isothiocyanates, produces disulfide Cys-S-S-R and -thiocyanoalanine, which cyclises to 2-thiazoline derivative (Figure 2.66). 

Pyridine sodium hydrogen carbonate Dithiocarbamic acid esters from isothiocyanates and mercaptans C,HiN/NaHCO, N C S NHC(S)SR... 

Fumigants of various structures also are employed to preserve harvested crops, corn, small grains, and so on, from insects and other pests. Vapam, the sodium salt of iV-methyl dithiocarbamic acid, decomposes or metabolizes in the soil to methyl isothiocyanate and provides a local fumigation of fungi, nematodes, and certain insects. 

Phenyl isothiocyanate has been prepared from thiocarbanilide by the action of phosphorus pentoxide, hydrochloric acid, iodine, phosphoric acid, acetic anhydride, and nitrous acid. It has also been prepared from ammonium phenyl dithiocarbamate by the action of ethyl chlorocarbonate, copper sulfate lead carbonate, lead nitrate, ferrous sulfate,and zinc sulfate. ... 

In order to obtain an isothiocyanate in the aliphatic series, a dithiocarbamate must be distilled with a salt of a heavy metal (HgCl2, FeCl3) (A. W. Hofmann). Here, in the case of diphenylthiourea, the distillation is carried out with concentrated hydrochloric acid. 

Ammonium dithiocarbamates can be prepared through reaction (11). With HC1 or H2S04 at lower temperatures the free acids are formed. Only one transition metal complex (37) is known, with a pseudo-octahedral coordination of Ni four sulfur atoms of the dithiocarbamate in the equatorial plane and two pyridine solvent molecules at the apical positions. Sulfides can be eliminated from monosubstituted dithiocarbamates to give isothiocyanates.53... 

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. 

Isothiocyanates (105) react with nucleophilic reagents such as amines, alcohols, thiols and acids to yield thioureas (104), thiono-or dithiocarbamates (114) (X = O or S), or amides (115) (Scheme 62). 

Aliphatic and aromatic isothiocyanates (43) may also be conveniently prepared by heating dithiocarbamates (3) with ethyl chloroformate (44) (Scheme 26). The intermediate (45) is stable in dilute acid but immediately decomposes in hot dilute potassium hydroxide, probably via a cyclic transition state in which the base... 

On the other hand, isothiocyanates are known to be reactive with a variety of food constituents, such as amines, amino acids, proteins, thiols, and alcohols, due to their electrophilic properties to give a variety of compounds, including thioureas and dithiocarbamates [32]. Despite their chemical nature, only limited information has been made available regarding the stability of isothiocyanates and the biological activity of reaction products of isothiocyanates with food constituents [33-35]. 

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