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The standard molar enthalpies of combustion and sublimation of benzothiazino-benzothiazine and benzoxazino-benzoxazine

✍ Scribed by Ramón Gudiño; Luis Alfonso Torres; Myriam Campos; Rosa Luisa Santillán; Norberto Farfán

Publisher
Elsevier Science
Year
1997
Tongue
English
Weight
190 KB
Volume
29
Category
Article
ISSN
0021-9614

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✦ Synopsis

The compounds cis-5a,6,11a,12-tetrahydro[1,4]benzothiazino [3,2-b][1,4]benzothiazine (BTB) and 5a,6,11a,12-tetrahydro[1,4]benzoxazino [3,2-b][1,4]benzoxazine(BOB) have been studied by oxygen bomb combustion calorimetry and by the Knudsen effusion method using a quartz-crystal microbalance. Based on the experimental results, the standard molar enthalpies of formation of the solid and gaseous compounds were determined. A summary of experimental and derived results at the temperature T = 298.15 K is shown below:

BTB BOB

DcU°m(cr)/(kJ•mol -1 ) -8580.9 2 5.9 -7040.9 2 5.9 DcH°m(cr)/(kJ•mol -1 ) -8593.3 2 6.0 -7043.2 2 6.0 DfH°m(cr)/(kJ•mol -1 ) 165.2 2 6.3 -180.9 2 6.3

288.5 2 6.4 -51.9 2 6.4 DatH°m(g)/(kJ•mol -1 ) 13860.2 2 8.9 14144.9 2 6.3

From a group-contribution scheme and from the experimental results, the group-contribution terms to the standard molar enthalpies of formation of the gaseous compounds for the molecular groups {C-(S)(N)(C)(H)} and {C-(O)(N)(C)(H)} were calculated as -76.1 kJ•mol -1 and -42.7 kJ•mol -1 , respectively. It is concluded that the standard molar enthalpy of formation in the gas phase is decreased by (340.4 2 9.0) kJ•mol -1 when two Cb-S bonds and two C-S bonds are substituted by two Cb-O bonds and two C-O bonds in the compound BTB to obtain BOB; here Cb refers to a carbon atom in the benzene ring.

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