The Generation and Properties of Tetrahedral Intermediates

Grieve, Duncan McLean Allan (1978) The Generation and Properties of Tetrahedral Intermediates. PhD thesis, University of Glasgow.

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The study of "tetrahedral intermediates" is reviewed. Studies by proton nuclear magnetic resonance spectroscopy (N.M.R.), of several ortho ester derivatives (acetoxy-dime-thoxy-methane, acetoxy-diethoxy-methane, 2-acetoxy-1,3-dioxolan, 2-acetoxy-4,4,5,5-tetramethyl-1,3-dioxolan and 2-chloroacetoxy-4,4,5,5-tetramethyl-1,3-dioxolan) have shown the existence of the postulated tetrahedral intermediates likely to be obtained from loss of the acetoxy or chloroacetoxy group followed by reaction with water. These intermediates have been shown to be observable over long periods at low temperatures and the rate constants for their decomposition have been calculated. The observation of one intermediate, 2-hydroxy-4,4,5,5-tetramethyl-1,3-dioxolan has also been carried out using 13C N.M.R. Attempts to synthesise other acetoxy species and other possible precursors (phenoxy and p-nitro-phenoxy derivatives, etc.) have all met with failure. Studies on the hydrolyses of other compounds have not resulted in the detection of any tetrahedral intermediates. Also no intermediates were detected in the reactions of various carbenium salts. The hydrolyses of 2,2-dimethoxytetrahydropyran and 2,2-diethoxytetrahydropyran yield delta-valerolactone, the alcohol (methanol or ethanol) and methyl or ethyl 5-hydroxyvalerate, indicating that the reaction is not specific as thought by Deslongchamps. The kinetics of the hydrolysis of benzaldehyde di-t-butyl acetal and alpha-acetoxy-alpha-t-butoxy-toluene has been studied in several acetate and one imidazole buffers. Both have been shown to hydrolyse by rate limiting decomposition of the hemiacetal at low pH by general buffer catalysis. Whereas no change in the rate determining step is observed for alpha-acetoxy-alpha-t-butoxy-toluene the hydrolysis of benzaldehyde di-t-butyl acetal shows complex two step kinetics (i.e. an induction period) over a very large pH range (ca 4-7) with a change in the rate determining step to hydrolysis of the acetal. No general buffer catalysis was observed at the higher pHs in the buffer used (imidazole).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry, Analytical chemistry
Date of Award: 1978
Depositing User: Enlighten Team
Unique ID: glathesis:1978-78803
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:53
Last Modified: 30 Jan 2020 14:53

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