Radiation Induced Incorporation of CO in Pure and Aqueous Methanol

Abstract

Pure and aqueous m ethanol were used for radiation induced incorporation of CO at elevated pressure (up to 15 bar). The initial yields (G,) of the main products in pure methanol under 15 bar CO and 1 bar N 20 were found to be: G, (formaldehyde) = 3.80 and G;(glycolic aldehyde) = 2.0. For aqueous (10" 2 mol • d m -3 ) methanol under 15 bar CO (dose: 0.557 kGy, pH -2): the yields were G (formaldehyde) = 5.44, G (glycolic aldehyde) = 4.0 and G (oxalic acid) = 7.7. At pH = 7 the yields were essentially lower, namely: G(formaldehyde) = 3.2, G(glycolic aldehyde) = 2.0, G(formate) = 3.8 and G (oxalate) = 5.0. Probable reaction-mechanisms for the product form ation are discussed.Based on previous carbonylation experiences of gamma-, electron-and UV-irradiated aqueous m etha nol under 1 bar CO (10" 3 mol • d m -3 CO) [1-6] the aim of the present work was to investigate this process at elevated CO pressures. Pure methanol as well as aqueous solutions were used for this purpose. Experimental R a diation S ource an d S o lu tio n P reparationA "Gammacell 220" (Atomic Energy of C anada Ltd.) was used as a 60Co-y-source, having a dose rate of 40 Gy • min " 1 *. The dosimetry was performed by means of a ferrous-copper dosimeter under the same experimental conditions [7].The applied methanol (p. A. Merck) was freshly distilled under argon atmosphere and kept in absence of air before use. High purity CO (Messer-Griesheim GmbH, Vienna) was used without further purification. The samples (50 ml) of pure or aqueous m ethanol were given into an open glass vessel which was fitted in an autoclave (see Figure 1). Prior to irradiation the solutions were deoxygenated by bubbling for 45 min with high purity argon and then saturated with CO at various pressures (1 -1 5 bar). A n a ly sisAliquots of the irradiated solutions were analyzed by spectrophotom etric methods for the yields of formaldehyde [8], glycolic aldehyde [9], glyoxal [10] and oxalic acid [11]. The total yield of the formed carboxylic acids was determined by titration with 10~3 mol • d m -3 N aO H . The individual measure ment of the formic acid was achieved by water steam distillation of an aliquot of the solution, followed by reduction with magnesia to formaldehyde in acid solution. By substrating the yield of the priorly mea sured aldehydes from the obtained total aldehyde am ount, the formic acid yield was determined. In ad dition to this, the G C-m ethod was applied in most cases, as well for the individual determ ination of gly col and other products. A GC-instrum ent (Carlo Erba 4160) equipped with split/splitless injector, FID and a 20 m glass capillary column with i.d. 0.32 mm coated with CW 20 M (high polymer carbowax, film thick ness 0.2 |im) was used. Hydrogen was applied as car rier gas (flow rate 2.6 ml/min). The injector tempera ture was 260 °C and that of the column 108 °C. The presented yields are mean values of the data obtained 0932-0784 / 94 / 0400-0617 $ 01.30/0. -Please order a reprint rather than making your own copy.