Hydrogen chloride alkynes

Hydrogen bromide (but not hydrogen chloride or hydrogen iodide) adds to alkynes by a free radical mechanism when peroxides are present m the reaction mixture As m the free radical addition of hydrogen bromide to alkenes (Section 6 8) a regioselectiv ity opposite to Markovmkov s rule is observed... 

The use of stronger acid conditions provides somewhat better synthetic yields of alkanes from alkynes. A useful method consists of treatment of the substrate with a combination of triethylsilane, aluminum chloride, and excess hydrogen chloride in dichloromethane.146 Thus, treatment of phenylacetylene with 5 equivalents of triethylsilane and 0.2 equivalents of aluminum chloride in this way at room temperature yields 50% of ethylbenzene after 1.5 hours. Diphenylacetylene gives a 50% yield of bibenzyl when treated with 97 equivalents of triethylsilane and 2.7 equivalents of aluminum chloride after 2.8 hours. Even 1-hexyne gives a mixture of 44% n -hexane and 7% methylpentane of undisclosed structure when treated with 10 equivalents of triethylsilane and 0.5 equivalent of aluminum chloride for 0.5 hour.146... 

Alkynes are readily acylated with acid chlorides under Friedel-Crafts conditions to form, in most cases, fram-p-chlorovinyl ketones through the corresponding vinyl cation intermediate [Eq. (8.16)]. The first study in 1935 reported low yields.11 Later in acylations with acyl triflates, p-keto vinyl triflates were obtained in satisfactory yields.123 When aroyl derivatives are used, the intermediate can undergo cyclization to form indenones. Chlorovinyl ketones formed from terminal alkynes may also react further losing hydrogen chloride to yield conjugated acetylenic ketones 11,13... 

A one-step synthesis of furo[3,2-c]- and furo[3,2-6]-pyridines has been realized using a cycloaddition reaction of an alkynic compound with 3,5-dichloropyridine 1-oxide (Scheme 15) (75JA3227). Formation of (75) probably proceeds through a 1,2-dihydropyridine (73) with a subsequent 1,5-sigmatropic shift to (74) elimination of hydrogen chloride yields... 

Nitrile imine cycloadditions provide access to pyrazolines and pyrazoles. Intramolecular cyclizations to alkynes were first reported in 1974.88 Perhaps the most useful method for generation of nitrile imines involves 1,3-elimination of hydrogen chloride from an a-chlorohydrazone. Tetrazoles and sydnones are also precursors to nitrile imines. 

Although these catalytic partial hydrogenations of alkynes may well be regarded as the procedure of choice for (Z)-alkenes,25 other catalytic systems have been explored. These include a sodium hydride-sodium alkoxide-nickel(n) acetate reagent,26 and a sodium borohydride-palladium chloride-polyethylene glycol system.27 Diisobutylaluminium hydride (DIBAL) has also been used for the conversion of alkynes into (Z)-alkenes.28 ( )-Alkenes are formed when the internal triple bond is reduced with sodium in liquid ammonia.29... 

The reaction of elemental silicon with a gaseous mixture of hydrogen chloride and unsaturated hydrocarbons such as alkenes (e.g., ethylene and propylene) and alkyne such as acetylene in the presence of copper catalyst also affords the corresponding organodichlorosilanes. 

A suggestion has been made that in some cases cycloaddition of an alkyne and loss of hydrogen chloride may be effectively synchronous.68... 

Nitrilimines (94), which are reactive 1,3-dipoles, undergo [3 + 2] cycloadditions with alkenic and alkynic dipolarophiles. Their use in the preparation of benzopyrazolooxazines and benzopyranopyrazoles, often in high yields, is illustrated in Scheme 33. The reactive intermediates, e.g. (96), are generated by elimination of hydrogen chloride from suitable substrates (95) and (97) (74TL269), or by photolysis of tetrazoles (98) (78JOC1664). Pyrazoles... 

CHLORCYAN (506-77-4) CNCl C-N-CL Noncombustible gas. Violent polymerization can be caused by chlorine or moisture. Violent reaction with alcohols, alkenes, and alkynes (violent exothermic reaction) acids, acid salts, amines, strong alkalis, olefins, strong oxidizers. Contact with acid forms toxic hydrogen cyanide gas. Mixtures with benzene or cyanogen halides yield hydrogen chloride. In cmde form, this chemical trimerizes violently if catalyzed by traces of hydrogen chloride or ammonium chloride, forming cyanuric chloride. Alkaline conditions will convert this chemical to... 

Hydrogen chloride adds to aryl alkynes in acetic acid to give mixtures of a-chlorostyrenes and the corresponding vinyl acetate. A vinyl cation, which is stabilized by the aryl substituent, is believed to be an intermediate. The ion pair formed by... 

Addition of hydrogen chloride to acetylene is technically a very important reaction and directions for it are laid down mainly in patents. Addition of HC1 to alkynes follows Markovnikov s rule. Whether addition of the first or the second mole of HC1 is the faster depends on the catalyst. The rate of reaction of acetylene and HC1 in the... 

A new approach to the synthesis of 1-chlorophosphirenes is afforded by the reaction of the phosphirane complex (309), presumably acting as a source of a phosphinidene, with disubstituted alkynes to give the complexed P-aminophos-phirenes (310), which, on treatment with hydrogen chloride, are converted to the related complexed 1-chlorophosphirenes (311). A key step is their selective... 

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