The reaction of free radicals with trichlorosilane

Bell, T. N.; Johnson, BB

doi:10.1071/ch9671545

Cited by 12 publications

(7 citation statements)

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“…Therefore, according to (11) we may determine the ratio k3/k4 simply from measurements of the initial ion currents of s and x and their initial rates of decrease during irradiation. Absolute calibrations relating observed ion currents to ion-source concentrations are not required.…”

Section: Resultsmentioning

confidence: 99%

Rate constants for the reactions of hydrogen atoms with some silanes and germanes

Austin¹,

Lampe²

1977

J. Phys. Chem.

136

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Publication costs assisted by the U. S. Energy Research and Development AdminlstrationRate constants for the reactions of H atoms, formed by mercury photosensitization of H2-substrate mixtures at 32 O C , with (CH3),SiH4-, and (C2HS),SiH4-, for n = 0, 1,2,3; with (CH3),SiD4-, for n = 0, 1; and with Si2H6, Si2D6, GeH4, and Ge2H6 have been determined in experiments involving the competitive reaction of H atoms with C2H4 and i-C4HB. Activation energies, estimated from these rate constants, have been combined with thermochemical data by means of a bond-energy-bond-order (BEBO) method of calculation to yield a consistent set of dissociation energies for Si-H bonds in the R,SiH4-, series of silanes for n = 0, 1, 2, 3.

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Section: Resultsmentioning

confidence: 99%

Rate constants for the reactions of hydrogen atoms with some silanes and germanes

Austin¹,

Lampe²

1977

J. Phys. Chem.

136

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“…The normally higher activation energy for H abstraction from hydrocarbons by CH, radicals as against CF, radicals leads to a difference in reactivity which may be reduced or even reversed with polar substrates such as H2S (8,13). The present results show that the CF, radical is slightly more reactive than the CH, radical to H2S; the literature indicates that CF, and CH, radicals show similar reactivities to MI (14,15) where AcF3/AcH, is 0.17, EcH, -EC-, is 1.8 kcal mole-' and kCF,/kcH3 is 1.4 at 150 "C, but that CF, radicals are less reactive than CH, to HBr (13,14,16) where AcH,/AcF, is 8.3, EcF, -Ec13, is 1.5 kcal mole-', and kcH,/kcF, at 150 "Cis 50, and to SiHC1, (17,18) where AcH,/AcF, is 20, EcH, -E,,, is 1.6 kcal mole-', and kCH,/k,,, is 2.7 at 150 "C. The Arrhenius parameters obtained here contain large standard errors since the temperature range investigated was small, however, if AcF,/AcH, is set equal to unity (8) then our rate-constants yield an activation energy of about 5 kcal mole-'. a more reasonable value than the low measured ones and one that compares well with the alkyl thiols.…”

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confidence: 99%

Abstraction of hydrogen from hydrogen sulfide by methyl radicals

Gray¹,

Herod²,

Leyshon³

1969

Can. J. Chem.

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The methyl radical attack on H,S has been investigated briefly using azomethane as the radical source. The results indicate that the previous rate-constants for the abstraction reaction are too high and that CF, radicals may react with H,S faster than CH, radicals.Canadian Journal of Chemistry, 47, 689 (1969) The reaction of methyl radicals with hydrogen sulfide has been investigated using the photolysis of azomethane as the source of methyl radicals. Previous workers generated methyl radicals from acetone (1) and acetaldehyde (2, 3) and obtained conflicting results. These earlier data are open to objection on several grounds: in the acetone work (1) the temperature range (50 to 200 "C) included a region (50 to 120 "C) where the Arrhenius relationship for methyl radical attack on acetone is non-linear; no account was taken of this. Furthermore, it was necessary to decompose large amounts of H2S; the assumption that SH radicals reformed H2S is unlikely since hydrogen sulfide was consumed during the reaction, other secondary reactions producing methane could be important. Secondary reactions may also have interfered in the work using acetaidehyde (2, 3) because the aldehyde decomposition is complex in the presence of thiols (4). Although the present work is not conclusive, it indicates that the previous rate-constants are too high.The experimental method was basically as has been described previously (5) although some modification was necessary because ethane and hydrogen sulfide cannot be separated by lowtemperature fractionation. In the bulk of the experiments the ethane content of the C,H6/H2S mixtures was estimated by gas chromatography using an alumina column which retained H2S. Two samples of azomethane were employed; one had been used In prevlous experiments (5) C.P. grade) was distilled through a trap at-80 "C. The purity of the reactants was checked by gas chromatography and mass spectrometry. From 10 experiments between 99 and 171 "C Arrhenius parameters for the reaction were found to be log,, A = 10.7 + 0.4 and E = 2.9 + 0.7 kcal m o l e ' , with log,, Ic = 9.20 at 150 "C. Support for these results is afforded by experiments where ethane was estimated differently; before measurement of the ethane, the C,H6/H2S mixture was treated with KOH pellets after which mass spectrometry indicated the con~plete removal of H2S. Using this technique, log,, k (kin cm3 mole-' s-l) was 8.87 at 147 "C, which can be compared with the corresponding figure of 9.19 by the first method. The agreement is satisfactory considering the rapid rates of reaction and the small amounts of ethane produced. H2S decomposition was limited to between 6 and 10% throughout the work.The present results are compared with previous work and related systems in Table I (all rateconstants are relative to Shepp's rate-constant for methyl radical combination (6)). It is clear that the present rate-constants are lower than previous values by about an order of magnitude at 150 "C. We have already drawn attention to possible sources of error in the ...

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“…No evidence was obtained for CF3Cl formation with the methylchlorosilanes, nor has previous work shown this to occur (3,5,7). There is a possibility that the competitive H abstraction process completely precludes chlorine abstraction.…”

Section: Chlorine Abstractionmentioning

confidence: 63%

“…Assuming that the reaction between CF, and / CH2Si-leads to insignificant amounts of CF,H, \ we have, from reactions [2] and [3] A test of this equation is seen in Fig. 1 the HFA pressure had no effect on k,/k3'12.…”

Section: Hydrogen Abstractionmentioning

confidence: 99%