Chloro-ethyne

CH2 CH C CH. Colourless gas with a sweet odour b.p. 5°C. Manufactured by the controlled low-temperature telomerization of ethyne in the presence of an aqueous solution of CuCI and NH Cl. Reduced by hydrogen to butadiene and, finally, butane. Reacts with water in the presence of HgSO to give methyl vinyl ketone. Forms salts. Forms 2-chloro-butadiene (chloroprene) with hydrochloric acid and certain metallic chlorides. 

E-(P-Alkylvinyl)phenyliodonium salts react with tetra-n-butylammonium halides to yield the correspondingly substituted Z-haloethenes (80-100% for chloro-, bromo- and iodo-derivatives) [41], In contrast, in the corresponding reaction with Z-(2-benzenesulphonyl-ethenyl)phenyliodonium salts, nucleophilic substitution occurs with retention of configuration to yield the Z-2-benzenesulphonyl-l-haloethenes [42], The ammonium fluorides fail to yield the fluoroethenes, but produce the ethynes by simple elimination [41]. Where carboxylic acids have low solubility in organic solvents, their conversion into the acid chlorides is frequently difficult. Phase-transfer catalysis not only allows the conversion to be effected rapidly, it also results in high yields of a wide range of acid chlorides [43]. 

In Section 10-5 we showed that ethyne is much less reactive toward chlorine than is ethene. The same is true for hydrogen chloride. Flowever, when hydrogen chloride adds to 3-butenyne, it adds to the triple bond instead of the double bond, thereby forming 2-chloro-1,3-butadiene instead of 3-chloro-1-butyne. With reference to the discussion in Section 13-2, explain why the order of reactivity of the double and triple bonds of 3-butenyne toward electrophilic reagents may be different from that of ethene and ethyne ... 

Another reaction pathway of great synthetic usefulness is the addition of halogen across bis(trimethylsilyl)ethyne (i2)30 to isolate trans-l,2-dihalogeno-l,2-bis(tri-methylsilyl)ethenes 29 and 30. Further halogenation leads to symmetrical (31, 32) and nonsymmetrical (33) ethane compounds the pyrolysis of 31 yields 1,1,2-tri-chloro-2-(trimethylsilyl)ethene (34) (Scheme 5). 

Via an amidoalkylation of bis(trimethylsilyl)ethyne (12) with methyl 2-chloro-N-ethoxycarbonylglycinate (57) under the influence of aluminum chloride the corresponding N-(ethoxycarbonyl)-a,a-TMS-ethynyl-glycinate (55) is isolated which is converted by means of lithium-di-isopropylamide (LDA) into a carbanion that reacts with alkylhalide to the substituted glycinate 59. Finally, after alkaline hydrolysis the unprotected a-acetylenic-a-aminoacid (60) (e. g. R = Benzyl a-ethynyl-a-phenyl-alanine is then obtained (Scheme 7). 

Treatment of 6-chloro-4-methylpyrrolo[2,3-6]pyridine with methoxide ion resulted in only 39% yield of the product from chloride displacement, even under very harsh conditions (300 °C). Ethynyl-ation of the halogenated pyrrolopyridines was also carried out. The reaction was successful using compound (73), after protection of the pyrrole nitrogen, and trimethylsilylethyne. However, with unsubstituted ethyne only the iodo derivative was reactive. In this case a disubstituted ethyne derivative (74) was obtained (Scheme 22) <68RCR55i>. 

The reaction between ethyne and phosgene has also been studied under photochemical conditions (>220 nm) [2185a]. As in the analogous reaction with ethene (see Section 10.1.2), the phosgene merely acts as a convenient source of chlorine radicals the principal products were CO, CHj=CHCl, 1-chloro-l, 3-butadiene, benzene and polymer trace amounts of HC Cl and CgHjCl were also detected [2185a]. 

The diazine substrate was prepared by reaction of the oxyanion of 2-bromophenol with 2-chloro-l,3-diazine followed by palladium(0)-mediated coupling with (trimethylsilyl)ethyne. 

Conversion of 2-Chloro-l,l-bis(Dimethylamino)Ethene into bis(Dimethylamino)Ethyne 95... 

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