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Question
What are KSH and HEM reagents and what are their functions?
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Solution
Dialkylthionocarbamates differ from the other two groups in distribution of bond from the key carbon. One of the first commercial O-N-dialkylthionocarbamates was Dow Z-200 that was an O-isopropyl-N-ethylthionocarbamate.
The synthesis of dialkylthionocarbamates is achieved by a number of different methods depending on the country where these reagents are produced. However, the principles are similar and two basic methods are described here. The first method is a two-stage reaction process, first reacting alkyl xanthate with alkyl halide to form ester of alkyixanthic acid as per the following reaction:
R−O−S||C|SK+CH3(halide)→R−O−S||C|S−CH3+K(halide)
In the second stage, the ester from the first reaction is treated with a primary amine and methylmercaptan, which is the by-product, is removed.
R−O−S||C|S−R1+R2NH2→R−O−S||C|NH−R1+R2SH
This is the method described by Hanis.
The second method includes the direct reaction of a xanthate with an alkyl amine in the presence of a catalyst (i.e. nickel or palladium salts). In this process, methylmercaptan is not removed. The chemical reaction is as follows:
R−O−S||C−SK+NH2−R1catalyst→R−O−S||C−NH−R1+KSH
Table 2.10 shows the physical characteristics of different thionocarbamates.
Xanthic acid can also be regarded as the acid ester of dithiocarbonic acid. Complete esterification may result in a rupture of the SH bond giving the neutral ester as ethyl-ethyl xanthate:
C2H5OC−(S)SC2H5
Diethyl xanthate has an ethereal odor reminiscent of leeks and can be distilled without decomposition at low pressure.
Alkyl esters of xanthic acid do not always involve the same hydrocarbon chain on both sides of the carbon atom, and it may also be possible that the atom that is double bonded to the central carbon could be the oxygen (giving an ester) of synt-dithiocarbonic acid. Therefore, three isomers are possible for each composition.
1. ROC||SSR1
2. R1OC||SSR
3. R1OCS||OR
The synthesis of dialkylthionocarbamates is achieved by a number of different methods depending on the country where these reagents are produced. However, the principles are similar and two basic methods are described here. The first method is a two-stage reaction process, first reacting alkyl xanthate with alkyl halide to form ester of alkyixanthic acid as per the following reaction:
R−O−S||C|SK+CH3(halide)→R−O−S||C|S−CH3+K(halide)
In the second stage, the ester from the first reaction is treated with a primary amine and methylmercaptan, which is the by-product, is removed.
R−O−S||C|S−R1+R2NH2→R−O−S||C|NH−R1+R2SH
This is the method described by Hanis.
The second method includes the direct reaction of a xanthate with an alkyl amine in the presence of a catalyst (i.e. nickel or palladium salts). In this process, methylmercaptan is not removed. The chemical reaction is as follows:
R−O−S||C−SK+NH2−R1catalyst→R−O−S||C−NH−R1+KSH
Table 2.10 shows the physical characteristics of different thionocarbamates.
Xanthic acid can also be regarded as the acid ester of dithiocarbonic acid. Complete esterification may result in a rupture of the SH bond giving the neutral ester as ethyl-ethyl xanthate:
C2H5OC−(S)SC2H5
Diethyl xanthate has an ethereal odor reminiscent of leeks and can be distilled without decomposition at low pressure.
Alkyl esters of xanthic acid do not always involve the same hydrocarbon chain on both sides of the carbon atom, and it may also be possible that the atom that is double bonded to the central carbon could be the oxygen (giving an ester) of synt-dithiocarbonic acid. Therefore, three isomers are possible for each composition.
1. ROC||SSR1
2. R1OC||SSR
3. R1OCS||OR
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