Hydrothermal carbon-carbon bond formation and disproportionations of C1 aldehydes: formaldehyde and formic acid.
Hydrothermal carbon-carbon bond formation and disproportionations of C1 aldehydes: formaldehyde and formic acid.
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DOI：
10.1021/jp052153k
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发表时间：
2005-07
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影响因子：
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通讯作者：
Saiko Morooka;Chihiro Wakai;N. Matubayasi;M. Nakahara
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文献类型：
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作者：
Saiko Morooka;Chihiro Wakai;N. Matubayasi;M. Nakahara
C1（碳一）醛，甲醛（HCHO）和甲酸（HCOOH = HOCHO）的水热反应途径和动力学，在225 ℃下，没有和与盐酸（HCl）高达0.6 M（摩尔dm（-3））进行了研究。所揭示的反应如下：（i）形成甲醇和甲酸的自缩合，两种甲醛之间的氧化还原反应，（ii）形成甲醇和碳酸的交叉缩合，甲醛和甲酸之间的氧化还原反应，以及（iii）酸催化的C-C键形成，产生乙醇酸（HOCH 2COOH）作为最简单的氨基酸甘氨酸的前体。反应iii是从C1醛、甲醛和甲酸的水热诱导的化学演变步骤。发现歧化反应I和II甚至在没有碱催化剂的情况下进行，这与经典的Cannizzaro反应不同。酸催化自交联反应（i）和C-C键的形成（iii），但阻碍交联反应（ii）。反应i、ii和iii的非催化和酸/碱催化路径的速率常数加和为2 x 10（-4）+（2 × 10（-3））[H+]，10（-4）+10（3）[OH-]，和（2 x 10（-3））[H+] M（-1）s（-1）;质子[H+]和氢氧根离子[OH-]的浓度以M表示。非催化（中性）交叉电离的速率常数比自电离的速率常数大1个数量级。通过调节甲醛、甲酸和HCl的浓度，在动力学分析的基础上控制反应途径，使乙醇酸和甲醇的生产占主导地位。当甲醛、HCl和甲酸以1：2：17的比例混合时，乙醇酸的转化率达到约90%。当向甲醛中加入过量的甲酸时，甲醛向甲醇的转化率达到约80%。
Hydrothermal reaction pathways and kinetics of C1 (carbon-one) aldehydes, formaldehyde (HCHO) and formic acid (HCOOH = HOCHO), are studied at 225 degrees C without and with hydrochloric acid (HCl) up to 0.6 M (mol dm(-3)). Reactions unveiled are the following: (i) the self-disproportionation forming methanol and formic acid, a redox reaction between two formaldehydes, (ii) the cross-disproportionation forming methanol and carbonic acid, a redox reaction between formaldehyde and formic acid, and (iii) the acid-catalyzed C-C bond formation producing glycolic acid (HOCH2COOH) as a precursor of the simplest amino acid, glycine. Reaction iii is a hydrothermally induced chemical evolution step from C1 aldehydes, formaldehyde and formic acid. Disproportionations i and ii are found to proceed even without base catalysts unlike the classical Cannizzaro reaction. Acid catalyzes the self-disproportionation (i) and the C-C bond formation (iii), but retards the cross-disproportionation (ii). The rate constants of noncatalyzed and acid/base-catalyzed paths for reactions i, ii, and iii are given additively as 2 x 10(-4) + (2 x 10(-3))[H+], 10(-4) + 10(3)[OH-], and (2 x 10(-3))[H+] M(-1) s(-1), respectively; the concentrations of proton [H+] and hydroxide ion [OH-] are expressed in M. The rate constant of the noncatalytic (neutral) cross-disproportionation is 1 order of magnitude larger than that of the self-disproportionation. The reaction pathways are controlled on the basis of the kinetic analysis to make the glycolic acid and methanol productions dominant by tuning the concentrations of formaldehyde, formic acid, and HCl. The conversion to glycolic acid reaches approximately 90% when formaldehyde, HCl, and formic acid are mixed in the ratio of 1:2:17. The conversion of formaldehyde to methanol reaches approximately 80% when formic acid is added in excess to formaldehyde.