乙醇辐解机理研究

INVESTIGATION OF THE MECHANISM OF GAMMA RADIOLYSIS OF ETHANOL

本文研究了氧、温度和4-甲基-4-苯基-2-戊酮(Mpp)对乙醇辐解的影响。Mpp在实验使用的浓度范围内对乙醛的G值没有影响,G(2,3-丁二醇)值随Mpp浓度增加而下降,最后达0.9恒值。使用Mpp求得原初过程形成的G_(H_2)=1.9,动力学处理求得G_H=2.4,k_(12)/k_(11)=(11.9±1.8)×10~3。实验证明Mpp清除了体系中的H原子,抑制了CH_3CHOH自由基的形成,从而抑制了2,3-丁二醇的生成,但不影响乙醛的产额。这一研究否定了传统文献所述的在γ辐解乙醇时相当量的羟乙基自由基歧化反应生成乙醛。本文还对乙醇γ辐解机理进行了讨论,并求得了乙醇辐解的物料平衡。

The effects of oxygen, temperature and 4-methyl-4-phenyl-2-pentanone (Mpp) on the gamma radiolysis of liquid ethanol have been investigated, The mechanism of the gamma radiolysis of ethanol has been discussed and the material balance has also been found. G(2,3-butanediol) values are 2.1 ±0.06 for N_2-saturated system and zero for air saturated system respectively Trace amount of oxygen in N_2 gas decreases G(2,3-butanediol) and increases G(CH_3CHO) at low absorbed dose (Fig. 1).The results show that 2,3-butanediol is formed in homogeneous liquid phase. In the presence of Mpp G(CH_3CHO) is a constant, but G(2,3-butanediol) falls down rapidly and approaches a limiting value (0.9) finally with the increase of Mpp concentration (Fig. 2). The results reveal that (1) CH_3CHOH radicals are formed by two processes at least and one of the precursors which produces CH_3CHOH radical can be scavenged by MPP; (2) acetaldehyde can unlikely be formed by the disproportionation reaction (2) and it might originate from the primary processes of the radiolysis of ethanol. The change in G(H_2) is similar to that of G(2,3-butanediol) in the presence of MPP (Fig.3). G(H_2) (1.9) which is independent of MPP con- centration is from the spur reations. The results show that MPP scavenges H atom in the system, which leads to the decrease of G(2,3-butanediol) and G(H_2). By using the kinetic formulas (13) and (14), we get G_H = 2.4 and k_(12)/k_(11) = (11.9 ± 1.8)×10~3. The above-mentioned results indicate that the traditional idea about the formation of acetaldehyde, namely certain amount of acetaldehyde (about 50%) is formed by CH_3CHOH diproportionation reaction, should be modified.