Thermodynamic properties of some methylphosphonyl dihalides from 15 to 335 °K

Abstract

M eas ur em ents of t h e heat capac it y of mC't h y lph osp ho ny l di flu o ri de (CH , P OF2) , methylphospho nyl di chl o rid e (CI-I 3PO Cl,), and m ethylphospho ny l chlo ro flu o ri de (CH aPOC lF) " 'ere m a de fro m a bo ut 15 to 335 oK by m eans of an adi abat ic calorim C'ter. These hi g hl y react ive and toxic su bstances were pu rifi ed in a com pletely closed glass appa rat us b.v co mbini ng s low crysta ll izat ion a nd fractional m eltin g proced lll·C'S. TI1l' puri t ies dC't('l" min ed b~' t hr fr eezin g-e ur vc mf't hod a re s hown to be generall y in agrC'emc nt with t hosE' valu es ohtain C' c\ h. v t he calo r.imetri c m et hod. From t he r('s ults of t he Iwat, m eaSll re m (' nt~, t he t ri p le-point k mperatu rc, heat o f fu sio n, and t heir co rrespo nclin g est im ated un certai nties \\"('I'e foun d to bp, res pectively, 236.34 ± 0.05 oJ\: and 1I ,878 ± 12 J / mo le fo r CH 3POF 2, 306. Triple-point tC'mpe rat ures obtain ed b.v thp fr cez ing-cu rve me t hod a rc in ag rec m ent \\" ith t he above val lies. A tab le of smoothed values of heat capac ity, enthalpy, entha lp y fun ct io n, ent ropy, G ib bs fr ee ene rgy, and G ibbs frp e e nergy fun ct ion fl'om 0 to 335 OK was obtained from t he d ata. T he ent ropy a nd its co rrespondin g pst im ated unce rt.ainty fo r C H3P OF2, CH 3POC I2, and CH3P OC IF in t heir respcc tive condenspd phase at 298. 1.5 o J( a nd sat urat ion press ure \Vas fo und to be 208.3 ± 0.3, 164.8 ± 0.3 , a nd 216.4 ± 0.4 J /d pg mole, rcs pecti ve ly. The entropies in the gaseo us state fLt 298. 15 OK a nd 1 atm press ure "-ere found to be 312.7 ± 3, 339.7 ± 3, a nd 335.0 ± 3 J /deg mol e, respecti ve ly.