CHEMISTRY

GIL’M KAMAI, B. D. CHERNOKAL’SKII

REFRACTIONS OF CERTAIN BONDS IN ORGANOARSENIC COMPOUNDS

(Presented by Academician A. E. Arbuzov, December 6, 1962)

In the chemical literature it has repeatedly been pointed out that it is advisable to use bond refractions (b.r.) for calculating molecular refraction (\(MR\)). The system of b.r., in comparison with the atomic refractions (\(AR\)) previously used for these purposes, reflects to a greater extent the physical essence of the polarizability of a molecule \((^{1,2})\), is more accurate \((^{1-4})\), and is more convenient to use because of the smaller number of parameters for compounds of polyvalent elements \((^{2,3})\). The most accurate method for calculating b.r. values in paraffins was proposed by K. Denbigh \((^{1})\) and was used by A. Fogel and co-workers \((^{3})\) to determine these quantities in various organic and organoelement compounds. A. Fogel’s data were subsequently supplemented by studies of other authors, chiefly for bonds of various elements with organogens \((^{4,5})\).

Table 1

B.r. \(C_{\text{aliph}}—\mathrm{As}\) in trialkylarsines, cm³/mol

In application to organoarsenic compounds, the b.r. system has hitherto not been used because of the absence of data on the b.r. of arsenic with organogens. Therefore, when calculating \(MR\) for organoarsenic compounds with the aid of \(AR\), it is necessary to use specific \(AR\) values for arsenic for each narrow class of compounds \((^{6-11})\).

In the present work, using literature data, the b.r. of carbon and oxygen with arsenic in its organic derivatives have been determined. The b.r. values of arsenic with other elements were calculated by subtracting from the experimentally found values, according to the Lorentz–Lorenz formula for the sodium \(D\) line, the known values \((^{3,12})\) of the b.r. present in the given compound. The true value of the b.r. was found for each type of compound as an arithmetic mean. From the calculation of the latter, data were excluded for those compounds in which the b.r. found differed from the arithmetic mean by more than 5%. The calculation error was estimated as the root-mean-square error.

For calculating the b.r. \(C_{\text{aliph}}—\mathrm{As}\) and \(O—\mathrm{As}\), the characteristics of symmetrical derivatives of trivalent arsenic were used: trialkylarsines (Table 1) and esters of arsenous acid (Table 2), respectively. For

For the C\(_{\text{aliph}}\)—As bond in trialkylarsines, the value of the bond refraction was found to be 4.51 cm\(^3\)/mol, and for the O—As bond in esters of arsenious acid, 3.91 cm\(^3\)/mol. Taking into account the ionic state of carbon in aromatic hydrocarbons (hybridization \(sp^2\) instead of \(sp^3\) in saturated compounds) and the possibility of interaction of the \(\pi\)-electrons of the benzene ring with the unshared pair of \(p\)-electrons of the arsenic atom, one might have expected a different polarizability of the C\(_{\text{arom}}\)—As bond as compared with the same property of the C\(_{\text{aliph}}\)—As bond. However, it was impossible to calculate the bond refraction of C\(_{\text{arom}}\)—As from \(MR_D\) for symmetrical triarylarsines in Ar\(_3\)As because of the absence of data on the specific gravity and refractive index of these compounds, which are solids at low temperatures. Therefore, for calculating the bond refraction of C\(_{\text{arom}}\)—As, experimentally found \(MR_D\) values of dialkylarylarsines Alk\(_2\)AsAr and alkyldiarylarsines AlkAsAr\(_2\) (Table 3), which under the same conditions are liquids, were used. The bond refraction C\(_{\text{arom}}\)—As in both types of compounds is approximately the same and averages 4.94 cm\(^3\)/mol.

Table 2

Bond refraction O—As in trialkyl arsenites, cm\(^3\)/mol

The bond refractions found were used to check the additivity of \(MR_D\) for esters of various arsenic acids. As it turned out, using the values found for the bond refractions C\(_{\text{aliph}}\)—As and O—As, one can obtain close agreement between the calculated and found \(MR_D\) values for esters of alkylarsinous acids. In the case of esters of dialkylarsinous acids, the average deviation between these quantities (0.28) is somewhat beyond the limits of the mean square error of calculation (0.24). Therefore, for accurate calculations of \(MR_D\) in esters of dialkylarsinous acids, a correction for molecular exaltation equal to +0.28 cm\(^3\)/mol should be introduced.

Table 3

Bond refraction C\(_{\text{arom}}\)—As in dialkylaryl- and alkyldiarylarsines, cm\(^3\)/mol

When using the system of bond refractions for calculating \(MR_D\) for four types of compounds (trialkylarsines, esters of arsenious acid, alkylarsinous and dialkylarsinous acids), it is sufficient to know six quantities—the bond refractions C—C, C—H, C—O, As—C and As—O, and the correction for molecular exaltation for esters of dialkylarsinous acids. Previously, for these purposes, seven atomic refractions were used—C, H, O and four specific atomic refractions of arsenic for each type of compound (\(^{8,9,11}\)). Therefore, extension of the bond-refraction system to organoarsenic compounds makes it possible—

Table 4

\(MR_D\) of esters of alkyl- and dialkylarsinic acids, cm\(^3\)/mol

will apparently reduce the number of characteristics required for calculating \(MR_D\) of the indicated substances.

Kazan Chemical-Technological Institute
named after S. M. Kirov

Received
30 XI 1962

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