Source:http://linkedlifedata.com/resource/pubmed/id/17198438
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rdf:type | |
lifeskim:mentions | |
pubmed:issue |
1
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pubmed:dateCreated |
2007-1-2
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pubmed:abstractText |
The kinetics of comproportionation of hypothiocyanous acid (HOSCN) and thiocyanate (SCN-) to give thiocyanogen ((SCN)2) in acidic aqueous solutions have been determined by double-mixing stopped-flow UV spectroscopy. Hypothiocyanite (OSCN-) was generated at pH 13 by oxidation of excess SCN- with hypobromite (OBr-), followed by a pH jump to acidic conditions ([H+] = 0.20-0.46 M). The observed pseudo-first-order rate constants exhibit first-order dependencies on [H+] and [SCN-] with overall third-order kinetics. The corresponding kinetics of hydrolysis of (SCN)2 have also been examined. Under conditions of high (and constant) [H+] and [SCN-], the kinetics exhibit second-order behavior with respect to [(SCN)2] and complex inverse dependences on [H+] and [SCN-]. Under conditions of low [H+] and [SCN-], the kinetics exhibit first-order behavior with respect to [(SCN)2] and independence with respect to [H+] and [SCN-]. We attribute this behavior to a shift in the rate-limiting step from disproportionation of HOSCN (second-order dependency on [(SCN)2]) to rate-limiting hydrolysis (first-order dependency on [(SCN)2]). Thus, we have determined the following equilibrium constant by the kinetic method: (SCN)2 + H2O HOSCN + SCN- + H+; Khyd = [HOSCN][SCN-][H+]/[(SCN)2] = khyd/kcomp = 19.8(+/-0.7) s-1/ 5.14(+/-0.07) x 103 M-2 s-1 = 3.9 x 10-3 M2.
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pubmed:language |
eng
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pubmed:journal | |
pubmed:citationSubset |
IM
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pubmed:chemical | |
pubmed:status |
MEDLINE
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pubmed:month |
Jan
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pubmed:issn |
0020-1669
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:day |
8
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pubmed:volume |
46
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
285-92
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pubmed:meshHeading | |
pubmed:year |
2007
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pubmed:articleTitle |
Kinetics and mechanism of the comproportionation of hypothiocyanous acid and thiocyanate to give thiocyanogen in acidic aqueous solution.
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pubmed:affiliation |
Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA.
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pubmed:publicationType |
Journal Article,
Research Support, U.S. Gov't, Non-P.H.S.,
Research Support, Non-U.S. Gov't
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