Reactions of the ethynyl radical. Part 2.—With alkenes

Abstract

Ethynyl radicals, from the 2537 A photolysis of bromoacetylene, have been reacted with c2-c6 monolefins with and without the addition of nitric oxide. Hydrogen abstraction occurs, and also addition of ethynyl to the n-bond followed by a displacement process giving conjugated or unconjugated enynes. The rates of these reactions have been measured relative to the formation of C4H2 by attack on bromoacetylene. The mechanism of the addition reaction is discussed.In part 1 of this series 1 we reported a study of the photolysis of the brornoacetylene + nitric oxide system, and some data derived from it, including relative rate constants for hydrogen abstraction from alkanes by ethynyl radicals. Our survey of the reactions of C2H has been extended to olefins, and the present paper describes reactions involving C 2 -4 6 monolefins and butadiene-l,3. EXPERIMENTAL M A T E R I A L SBromoacetylene and nitric oxide were prepared or purified as described previously.1 The olefins, Phillips Research Grade (ethylene, propene, the 4 butenes, butadieiie-l,3, pentene-1 and hexene-1) and American Petroleum Institute standards (pentene-2, hexene-2, hexene-3, 3-methylbutene-1 and cyclopentene) were all purer than 99.8 %, and were used after degassing and low-temperature distillation. The purities of 3,3-dirnethylbutene-1 (K and K), 2-methylbutene-1 and 2-niethylbutene-2 (Matheson Coleman and Bell), dimet h ylbut ene-2 (Chemical Procurement Labs . ) and met hylenec yclobut ane (Aldrich) were checked by gas chromatography (GLC) using a 16-ft. dimethyl sulpholane/celite column, and were improved t o 99.5 %+ , where necessary. C2D4 and CH2CD2 (Merck, Montreal), CD3CHCH2 (Volk Radiochemical), CH3CFCH2 and CF3CFCF2 (Peninsular Chemresearch)were treated similarly using a 6-ft. silica gel column. The C2D4 contained 3 % C2D3H; the isotopic purities of the other deuterated compounds were not checked.Methylbutenyne (K and K) was purified by GLC using the dimethyl sulpholane column. 1-Pentenyne-4 and cis and trans 3-pentenyne-1 were made by esterifying 1-pentynol-4 with acetic anhydride, and pyrolyzing the acetate.2 The three isomers (formed in similar yields) were separated by GLC using an 1 8-ft. tris-(cyanoethoxy)-propanelfirebrick column. The remaining isomer, 1-pentenyne-3, was made 3 by bubbling butenyne into a well-stirred solution of sodium in liquid ammonia, and adding iodomethane ; it was similarly purified. The structures of all five isomers were identified by n.m.r., with further confirmation by i.r. for the cis-3,1 isomer.4 Repurified samples were used to obtain mass-spectrometric (MS) cracking patterns (see appendix). PROCEDUREPhotolysis and analysis procedures were as described for runs with added alkane in part 1.1 Runs without added NO contained 7-5 torr BrC2H ; the others used 15 torr of 1221

The Photolysis of 3,3,3-Trifluoropropyne

“…The formation of butadiyne by the reaction of ethynyl radicals with acetylenes in the presence of nitric oxide has been observed previously (21,22). The absence of butadiyne among the products of the uninhibited reaction, also observed previously in similar systems (21,22), may be due to consumption of this product by free radicals or to actual participation of NO in its formation.…”

“…The absence of butadiyne among the products of the uninhibited reaction, also observed previously in similar systems (21,22), may be due to consumption of this product by free radicals or to actual participation of NO in its formation. This aspect of the problem requires further work as does the problem of the origins of the C,HF and C,H,.…”

Formation of fulvene in the reaction of C2H with 1,3-butadiene

“…Upon photolysis of BrC 2 H, 1,3-butadiyne forms by reaction of the photolytically produced C 2 H radical with the radical precursor via the mechanism outlined in Scheme 1 in Fig. 4 [55]. The peaks at m/z = 39 and 52 have been identified as propargyl radicals [56] (C 3 H 3 ), Fig.…”

Photolyse du butyne-2 dans la région de l'uv sous vide

“…I1 faut se rappeler que I'absorption dans cette region met en jeu des etats Rydberg, et le comportement de la molecule photoexcitee peut Ctre particulier. Le haut rendement en hydrogene atomique favorise cependant les reactions [14] et [15]. For personal use only.…”