Ton Overeem

Photoinitiators and photoinitiation Part 11. The photodecomposition of some O-acyl 2-oximinoketones

The photodecomposition of several O-acyl 2-oximinoketones was studied using electron spin resonance and proton nuclear magnetic resonance chemically induced dynamic nuclear polarization techniques. Primary NO bond cleavage into α-ketoiminyl and acyloxy radicals from the triplet excited state was observed in all cases. α-Ketoiminyl radicals observable at T < −70°C underwent rapid fragmentation into a benzoyl radical and a nitrile at temperatures exceeding −60°C. Chemical evidence was provided by radical trapping using a thiol and a stable nitroxyl respectively. These experiments also showed that, for most O-acyl 2-oximinoketones 1, [E] ⇌ [Z] photisomerization was the major process, whereas for O-acyl 2-oximinoketones 2 photodecomposition was almost exclusive.

A study of the photodecomposition products of an acylphosphine oxide and 2,2-dimethoxy-2-phenylacetophenone

Abstract The photodecomposition of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,2-dimethoxy-2-phenylacetophenone was investigated under normal ultra-violet curing conditions. The rate of formation and the identity of the many photodecomposition products produced by each photoinitiator were similar, whether amines (triethylamine or N-methyldiethanolamine) were present or not. Experimental evidence indicates that the role of amines is predominantly one of oxygen scavenger. It was also established that the shelf-life (stability) of the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide is short when present in an epoxydiacrylate N- methyldiethanolamine ultra-violet curable formulation. The decomposition products identified indicated that this is due to the occurrence of transesterification and hydrolysis reactions.

Photoinitiators and photoinitiation 10. The photodecomposition of some carboxylic esters of α-hydroxymethylbenzoin

Abstract The photodecomposition of some carboxylic esters of α-hydroxymethylbenzoin was studied using electron spin resonance (ESR) and proton nuclear magnetic resonance-chemically induced dynamic nuclear polarization ( 1 H NMR-CIDNP) techniques. Exclusive α-cleavage into benzoyl and α-hydroxy-α-acyloxymethylbenzyl radicals through the triplet excited state was observed. The α-hydroxy-α-acyloxymethylbenzyl radicals mainly undergo disproportionation with the other radicals present to give benzoylmethyl carboxylates. Elimination of carboxylic acids from the α,α-disubstituted benzyl radicals occurs to some extent, but at a much lower rate than the elimination of sulphonic acids from the corresponding α-hydroxy-α-sulphonyloxymethylbenzyl radicals generated from the sulphonic esters of α-hydroxymethylbenzoin.

The Isolation of Proteins from Whey with a New Strongly Acidic Silica-Based Ion Exchanger

Abstract A new type of strongly acidic ion exchanger based on macroporous silica coated with a thin layer of hydrophilic copolymer with sulphonic acid groups has been evaluated. The coating is crosslinked and covalently linked to the silica surface via diol groups. The performance for isolation of proteins from whey of the new ion exchanger and Spherosil S were compared using both batchwise adsorption and column operations with reconstituted whey. Higher breakthrough capacities were observed for the new ion exchanger than for Spherosil S. Excellent column operational lifetimes were found for the new product. A procedure is described to restore the original adsorption capacity of fouled columns.

The photoinduced α-cleavage of α-bromomethylbenzoin: the generation and behaviour of β-bromoketyl radicals

Abstract The photodecomposition of α-bromomethylbenzoin was studied by electron spin resonance and by radical trapping using I-dodecanethiol and a stable nitroxyl (TMPO) respectively. Photoinduced α-cleavage into benzoyl and α-hydroxy-α-bromomethylbenzyl (β-bromoketyl) radicals is observed. The β-bromoketyl radicals are found to undergo an extremely fast elimination of hydrogen bromide to give benzoylmethyl radicals. These β-bromoketyl radicals are also generated by hydrogen-abstraction from 2-bromo-1-phenyl-ethanol using triplet excited benzophenone. The only products observed are ‘unchanged’ benzophenone, acetophenone and hydrogen bromide. The same result is obtained on irradiation of 2-bromoacetophenone in the presence of benzhydrol. Possible mechanisms and implications are discussed.

Photoinitiators and photoinitiation. Part 13. The photodecomposition of sulphonic esters of α-hydroxymethylbenzoin ethers

Abstract The photodecomposition of some sulphonic esters of α -hydroxymethylbenzoin ethers is examined using ESR and radical trappingtechniques. Photoinduced α -cleavage into benzoyl and α -alkoxy- α -sulphonyloxymethylbenzyl radicals from a short-lived triplet excited state is observed. The α , α -disubstituted benzyl radicals undergo subsequent fragmentation, generating benzoylmethylradicals and sulphonic acids at a rate k el 7 s −1 . The fate of the alkyl ether part of the α,α-disubstituted benzyl radicals after elimination of sulphonic acid is unknown at present.