Nucleophilic ion pairs. Part II. Micellar catalysis of proton abstraction by hydroxamate anions

Seiji Shinkai, Toyoki Kunitake

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Hydroxamate anions in a cat ionic (cetyltrimethylammonium bromide. CTAB) micelle were found to serve as excellent catalysts for proton abstraction from oc-ketols. Proton removal from benzoin by N-methylmyristohydroxamateanion (MMHA) in the CTAB micelle was 3 500 times faster than the corresponding reaction in a non-micellar system, and 56 times faster than that by the much more basic hydroxide ion. A similar, dramatic rate enhancement was attainable by addition of small amounts of CTAB or methyltri-n-octylammonium chloride (TMAC) to MMHA solubilized in aqueous non-ionic micelles. On the other hand, the MMHA,NEt 4 ion pair in organic solvents was also effective for proton abstraction. MMHA,NEt4 in highly dehydrated acetonitrile gave a rate 103 higher than that in aqueous media. Minute amounts of H 2O and Nal efficiently quenched the reaction in dry organic solvents, and it was inhibited in protic solvents. It was suggested from these experimental data that the rate enhancement of MMHA in the presence of a cationic micelle largely stems from formation of a hydrophobic ion pair which is loose and desolvated in the micellar phase.

Original languageEnglish
Pages (from-to)980-985
Number of pages6
JournalJournal of the Chemical Society, Perkin Transactions 2
Issue number9
DOIs
Publication statusPublished - Jan 1 1976

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Micelles
Catalysis
Anions
Protons
Ions
Organic solvents
Benzoin
Chlorides
Catalysts
cetrimonium

All Science Journal Classification (ASJC) codes

  • Chemistry(all)

Cite this

Nucleophilic ion pairs. Part II. Micellar catalysis of proton abstraction by hydroxamate anions. / Shinkai, Seiji; Kunitake, Toyoki.

In: Journal of the Chemical Society, Perkin Transactions 2, No. 9, 01.01.1976, p. 980-985.

Research output: Contribution to journalArticle

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AB - Hydroxamate anions in a cat ionic (cetyltrimethylammonium bromide. CTAB) micelle were found to serve as excellent catalysts for proton abstraction from oc-ketols. Proton removal from benzoin by N-methylmyristohydroxamateanion (MMHA) in the CTAB micelle was 3 500 times faster than the corresponding reaction in a non-micellar system, and 56 times faster than that by the much more basic hydroxide ion. A similar, dramatic rate enhancement was attainable by addition of small amounts of CTAB or methyltri-n-octylammonium chloride (TMAC) to MMHA solubilized in aqueous non-ionic micelles. On the other hand, the MMHA,NEt 4 ion pair in organic solvents was also effective for proton abstraction. MMHA,NEt4 in highly dehydrated acetonitrile gave a rate 103 higher than that in aqueous media. Minute amounts of H 2O and Nal efficiently quenched the reaction in dry organic solvents, and it was inhibited in protic solvents. It was suggested from these experimental data that the rate enhancement of MMHA in the presence of a cationic micelle largely stems from formation of a hydrophobic ion pair which is loose and desolvated in the micellar phase.

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