Mechanism of Hydrocarbon Functionalization by an Iodate/Chloride System: The Role of Ester Protection

Nichole A. Schwartz; Nicholas C. Boaz; Steven E. Kalman; Thompson Zhuang; Jonathan M. Goldberg; Ross Fu; Robert J. Nielsen; William A. Goddard; John T. Groves; T. Brent Gunnoe

doi:10.1021/acscatal.7b04397

Mechanism of Hydrocarbon Functionalization by an Iodate/Chloride System: The Role of Ester Protection

Nichole A. Schwartz, Nicholas C. Boaz, Steven E. Kalman, Thompson Zhuang, Jonathan M. Goldberg, Ross Fu, Robert J. Nielsen, William A. Goddard, John T. Groves, T. Brent Gunnoe

Research output: Contribution to journal › Article › peer-review

25 Scopus citations

Abstract

Mixtures of chloride and iodate salts for light alkane oxidation achieve >20% yield of methyl trifluoroacetate (TFA) from methane with >85% selectivity. The mechanism of this C-H oxygenation has been probed by examining adamantane as a model substrate. These recent results lend support to the involvement of free radicals. Comparative studies between radical chlorination and iodate/chloride functionalization of adamantane afford statistically identical 3°:2° selectivities (∼5.2:1) and kinetic isotope effects for C-H/C-D functionalization (k_H/k_D = 1.6(3), 1.52(3)). Alkane functionalization by iodate/chloride in HTFA is proposed to occur through H-atom abstraction by free radical species including Cl^• to give alkyl radicals. Iodine, which forms by in situ reduction of iodate, traps alkyl radicals as alkyl iodides that are subsequently converted to alkyl esters in HTFA solvent. Importantly, the alkyl ester products (RTFA) are quite stable to further oxidation under the oxidizing conditions due to the protecting nature of the ester moiety.

Original language	English (US)
Pages (from-to)	3138-3149
Number of pages	12
Journal	ACS Catalysis
Volume	8
Issue number	4
DOIs	https://doi.org/10.1021/acscatal.7b04397
State	Published - Apr 6 2018

All Science Journal Classification (ASJC) codes

Catalysis
General Chemistry

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title = "Mechanism of Hydrocarbon Functionalization by an Iodate/Chloride System: The Role of Ester Protection",

abstract = "Mixtures of chloride and iodate salts for light alkane oxidation achieve >20% yield of methyl trifluoroacetate (TFA) from methane with >85% selectivity. The mechanism of this C-H oxygenation has been probed by examining adamantane as a model substrate. These recent results lend support to the involvement of free radicals. Comparative studies between radical chlorination and iodate/chloride functionalization of adamantane afford statistically identical 3°:2° selectivities (∼5.2:1) and kinetic isotope effects for C-H/C-D functionalization (kH/kD = 1.6(3), 1.52(3)). Alkane functionalization by iodate/chloride in HTFA is proposed to occur through H-atom abstraction by free radical species including Cl• to give alkyl radicals. Iodine, which forms by in situ reduction of iodate, traps alkyl radicals as alkyl iodides that are subsequently converted to alkyl esters in HTFA solvent. Importantly, the alkyl ester products (RTFA) are quite stable to further oxidation under the oxidizing conditions due to the protecting nature of the ester moiety.",

author = "Schwartz, {Nichole A.} and Boaz, {Nicholas C.} and Kalman, {Steven E.} and Thompson Zhuang and Goldberg, {Jonathan M.} and Ross Fu and Nielsen, {Robert J.} and Goddard, {William A.} and Groves, {John T.} and Gunnoe, {T. Brent}",

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AU - Schwartz, Nichole A.

AU - Boaz, Nicholas C.

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AU - Zhuang, Thompson

AU - Goldberg, Jonathan M.

AU - Fu, Ross

AU - Nielsen, Robert J.

AU - Goddard, William A.

AU - Groves, John T.

AU - Gunnoe, T. Brent

PY - 2018/4/6

Y1 - 2018/4/6

N2 - Mixtures of chloride and iodate salts for light alkane oxidation achieve >20% yield of methyl trifluoroacetate (TFA) from methane with >85% selectivity. The mechanism of this C-H oxygenation has been probed by examining adamantane as a model substrate. These recent results lend support to the involvement of free radicals. Comparative studies between radical chlorination and iodate/chloride functionalization of adamantane afford statistically identical 3°:2° selectivities (∼5.2:1) and kinetic isotope effects for C-H/C-D functionalization (kH/kD = 1.6(3), 1.52(3)). Alkane functionalization by iodate/chloride in HTFA is proposed to occur through H-atom abstraction by free radical species including Cl• to give alkyl radicals. Iodine, which forms by in situ reduction of iodate, traps alkyl radicals as alkyl iodides that are subsequently converted to alkyl esters in HTFA solvent. Importantly, the alkyl ester products (RTFA) are quite stable to further oxidation under the oxidizing conditions due to the protecting nature of the ester moiety.

AB - Mixtures of chloride and iodate salts for light alkane oxidation achieve >20% yield of methyl trifluoroacetate (TFA) from methane with >85% selectivity. The mechanism of this C-H oxygenation has been probed by examining adamantane as a model substrate. These recent results lend support to the involvement of free radicals. Comparative studies between radical chlorination and iodate/chloride functionalization of adamantane afford statistically identical 3°:2° selectivities (∼5.2:1) and kinetic isotope effects for C-H/C-D functionalization (kH/kD = 1.6(3), 1.52(3)). Alkane functionalization by iodate/chloride in HTFA is proposed to occur through H-atom abstraction by free radical species including Cl• to give alkyl radicals. Iodine, which forms by in situ reduction of iodate, traps alkyl radicals as alkyl iodides that are subsequently converted to alkyl esters in HTFA solvent. Importantly, the alkyl ester products (RTFA) are quite stable to further oxidation under the oxidizing conditions due to the protecting nature of the ester moiety.

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Mechanism of Hydrocarbon Functionalization by an Iodate/Chloride System: The Role of Ester Protection

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