The photostabilities of various ferrocene derivatives in solution have been studied as a function of solvent and, to a lesser extent, of incident wavelength. Some substituted ferrocenes, like ferrocene itself, did not decompose in methanol solution on exposure to near-ultraviolet light or sunlight; the remainder decomposed rapidly. Solutions of some derivatives in a number of other solvents also proved susceptible to photolysis. Qualitative evidence suggests that solute-solvent interaction leads to photochemically unstable species. Ferric ions do not appear to be formed in significant quantities during the degradative processes.Of the substituted ferrocenes investigated in this work, p-acetophenylferrocene appears to have considerable merit as a relatively stable and therefore protective light absorber. None of the derivatives, however, is as stable as ferrocene, which is prohibitively volatile for most practical applications.

Bromoacetylene has been used as a photolytic source of ethynyl radicals and bromine atoms. A polymerization chain initiated by bromine atoms is prevented by the addition of nitric oxide, which reacts with the 1 : 2-dibromovinyl radical as described previously.4 Ethynyl is not scavenged by nitric oxide, and reacts with bromoacetylene by hydrogen-abstraction or halogen-displacement mechanisms. Rate-constants have been measured relative to this displacement process for hydrogenabstraction from certain alkanes and cycloalkanes.

The competitive photobrorninations of the following pairs of reactants have been studied in the vapour phase : C&+C&F, CH3F+CH2F2, CH4fCH2F2, C~FSH+CF~H and CH4fC2F5H. The results are internally consistent and for the H abstraction reactions, we obtain Br -t CH4, Br + CH3Fy Br + CH2F2, Br + CF3H, Br + C2F5Hy = 0.56 f0-03 exp (2480 f40/RT) ~C H ~F / ~C H ~F ~ = 2-01 i-0.23 exp (780&1OO/RT), ~c H ~F ~/ ~c H , , = 0-24f0-01 exp (2000&40/RT), ~c ~F ~H , / ~c F ~H = 0-81 k0.05 exp (3040f60/RT), k a / k ~~~~~ = 8.88 ~t 0 . 8 5 exp (720 &90/RT). These results in conjunction with activation energies for the reverse reactions, where available, lead to D(CH3-H) = 103f1, D(CF3-H) = 105fl and D(CFJ--H)-D(CH~-H) = 2.210-5, all in kcal mole-1. Also D(H-CH2F) Q 103, D(H-CHF& 103 and D(C2F5-H) Q 102 kcal mole-1. These dissociation energies are compared with other values in theliterature. The theoretical A factors for the reactions based on transition state theory agree well with the experimental data.The effect of halogen substituents on hydrogen abstraction reactions in general is discussed.

No 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