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All posts Subject: Pb(IV)Acetate: alpha/beta-methylstyrenes to P2P Please login to post

Rhodium
(Chief Bee)
05-03-04 22:54
No 504638
User Picture Pb(IV)Acetate: alpha/beta-methylstyrenes to P2P
(Rated as: excellent)

This is a rather long article, and the products shown in the pictures may look unfamiliar to many, but this is actually a really neat procedure. In short, both α-Methylstyrene and β-Methylstyrene (propenylbenzene) can be oxidized by lead(IV)acetate to similar product mixtures, the great majority of which are substances which will form phenyl-2-propanone (P2P) upon acid hydrolysis. The article also contains procedural details for several similar transformations (Prevost oxidation for example).

Reactions of Lead Tetra-acetate. Part XV. The Oxidation of α- and cis- and trans-β-Methylstyrene
R. O. C. Norman and C. B. Thomas
J. Chem. Soc. (B) 994-1005 (1968) (https://www.rhodium.ws/pdf/p2p.lead4acetate.pdf)

Abstract
Like styrene, α-methylstyrene and cis- and trans- (β-methylstyrene are oxidised by lead tetra-acetate by concurrent homolytic and heterolytic pathways. The relative significance of the two types of reaction is dependent on the conditions. For α-methylstyrene, the relative importance of the homolytic reaction is much smaller than for styrene. at least in part because the heterolytic reaction is so much faster (k_rel = 19), whereas for the β-methylstyrenes both types of reaction are much slower than for styrene. The heterolytic reaction occurs by way of an adduct for which there competitive reaction paths, namely, the migration of the phenyl group and the formation of a acetoxonium ion; for α-methylstyrene, the former dominates whereas, for the β-methylstyrenes, products to be expected from phenyl-migration could not be detected, and an explanation for this difference is suggested. The acetoxonium ion can be opened by reaction with water to give hydroxyacetates, and this has enabled the stereochemistry of the heterolytic reactions of the β-methyl styrenes with lead tetra-acetate to be studied; the results are compared with those for oxidation by the 'wet' Prévost procedure. Autoxidation is catalysed under the reaction conditions, and gives hydroxyacetates and the aromatic carbonyl compounds formed by cleavage of the olefinic bond.

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		Rhodium (Chief Bee) 05-03-04 22:54 No 504638				Pb(IV)Acetate: alpha/beta-methylstyrenes to P2P (Rated as: excellent)
						This is a rather long article, and the products shown in the pictures may look unfamiliar to many, but this is actually a really neat procedure. In short, both α-Methylstyrene and β-Methylstyrene (propenylbenzene) can be oxidized by lead(IV)acetate to similar product mixtures, the great majority of which are substances which will form phenyl-2-propanone (P2P) upon acid hydrolysis. The article also contains procedural details for several similar transformations (Prevost oxidation for example). *Reactions of Lead Tetra-acetate. Part XV. The Oxidation of α- and cis- and trans-β-Methylstyrene* R. O. C. Norman and C. B. Thomas J. Chem. Soc. (B) 994-1005 (1968) (https://www.rhodium.ws/pdf/p2p.lead4acetate.pdf) Abstract Like styrene, α-methylstyrene and cis- and trans- (β-methylstyrene are oxidised by lead tetra-acetate by concurrent homolytic and heterolytic pathways. The relative significance of the two types of reaction is dependent on the conditions. For α-methylstyrene, the relative importance of the homolytic reaction is much smaller than for styrene. at least in part because the heterolytic reaction is so much faster (k_rel = 19), whereas for the β-methylstyrenes both types of reaction are much slower than for styrene. The heterolytic reaction occurs by way of an adduct for which there competitive reaction paths, namely, the migration of the phenyl group and the formation of a acetoxonium ion; for α-methylstyrene, the former dominates whereas, for the β-methylstyrenes, products to be expected from phenyl-migration could not be detected, and an explanation for this difference is suggested. The acetoxonium ion can be opened by reaction with water to give hydroxyacetates, and this has enabled the stereochemistry of the heterolytic reactions of the β-methyl styrenes with lead tetra-acetate to be studied; the results are compared with those for oxidation by the 'wet' Prévost procedure. Autoxidation is catalysed under the reaction conditions, and gives hydroxyacetates and the aromatic carbonyl compounds formed by cleavage of the olefinic bond. ^{The Hive - Clandestine Chemists Without Borders}

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