Acetic acid, formation

When growing on grape sugars, heterofermentative LAB produce varying amounts of ethanol, acetic acid, in addition to lactic acid, and CO2 (see Fig. 1-4B). Homofermentative species are also able to utilize hexose sugars but do so via the EMP pathway where D-lactic acid is produced by reduction of pyruvate. The latter group, however, may produce both acetic and lactic acids when growing on pentoses (Sponholz, 1993). 

Acetic acid produced by LAB is often sensorially different from that resulting from growth of acetic acid bacteria (AAB). In the latter case, VA is often perceived as a mixture of acetic acid and ethyl acetate, whereas with LAB, the ethyl acetate component is either missing or present at very low levels (Henick-Kling, 1993). Sensorially, acetic acid, in the absence of the acetate ester, is less easily detected even at levels well in excess of legal limits. 

Aside from potential sensory implications, acetic acid and associated products of LAB metabolism represent potent inhibitors to fermentatively growing Saccharomyces, delaying the onset of fermentation and potentially causing fermentation to stick (see previous discussion of Microbial Antagonism). At pH 3.5, bacterial carbohydrate metabolism (Peynaud and Domercq, 1968) or MLF (Giannakopoulis et al., 1984 Zeeman et al., 1982) yielded higher concentrations of acetic acid than parallel lots at a lower pH. 

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The results shown in Figure 4 indicate that the oxygen dependency of the acetic acid formation is higher than that of the citraconic anhydride formation. Therefore, use of a low oxygen concentration is beneficial to the selectivity to citraconic anhydride, though it is disadvantageous to the reaction rate. 

As may be seen in Figures 5 and 6, when iron phosphate is used as the catalyst, the selectivity is dependent largely on the reaction temperature. Therefore, the activation energy for the citraconic anhydride formation is considered to be much lower than that for the acetic acid formation. Indeed, the selectivity to acetic acid decreases steadily with a decrease in the temperature. However, the selectivity to citraconic anhydride shows a maximum at about 200 C. Possibly, the vaporization of pyruvic acid may become difficult at temperatures below 200°C. 

Infrared spectroscopy has also been employed to follow the formation of acetaldehyde and acetic acid on Pt during ethanol electro-oxidation. On the basal planes, acetaldehyde could be observed starting at about 0.4 V (vs. RHE), well before the onset of CO oxidation, while the onset of acetic acid formation closely follows CO2 formation [Chang et al., 1990 Xia et al., 1997]. This is readily explained by the fact that both CO oxidation and acetic acid formation require a common adsorbed co-reactant, OHads, whereas the formation of acetaldehyde from ethanol merely involves a relatively simple proton-electron transfer. 

Rowell etal. (1987b) produced PF-bonded flakeboard from acetylated southern pine (21.6 % WPG) or aspen (17.6 % WPG) flakes. This was not completely resistant to attack by termites Reticulitermes flavipes) in a 4-week test. It was thought that acetylation was less effective in preventing termite attack than other chemical modifications because cellulose decomposition in the intestines of termites leads to acetic acid formation in any case. 

Fig. 7. Enzyme-coupled assay in which the hydrolase-catalyzed reaction releases acetic acid. The latter is converted by acetyl-CoA synthetase (ACS) into acetyl-CoA in the presence of (ATP) and coenzyme A (CoA). Citrate synthase (CS) catalyzes the reaction between acetyl-CoA and oxaloacetate to give citrate. The oxaloacetate required for this reaction is formed from L-malate and NAD in the presence of L-malate dehydrogenase (l-MDH). Initial rates of acetic acid formation can thus be determined by the increase in adsorption at 340 nm due to the increase in NADH concentration. Use of optically pure (Ry- or (5)-acetates allows the determination of the apparent enantioselectivity i app i81)-...

Scheme 8.1 Acetic acid formation from CO, the role of CODH and tetrahydrofolate (THF).

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

Figure 7 shows the results of methyl acetate carbonylation in the presence of water. Methanol and dimethyl ether were formed up to 250 C suggesting that hydrolysis of methyl acetate proceeded. With increasing reaction temperature, the yield of acetic acid increased remarkably, while those of methanol and dimethyl ether decreased gradually. Figure 8 shows the effects of partial pressures of methyl iodide, CO, and methyl acetate in the presence of water. The rate of acetic acid formation was 1.0 and 2.7 order with respect to methyl iodide and CO, respectively. Thus, the formation of acetic acid from methyl acetate is highly dependent on the partial pressure of CO. This suggests that acetic acid is formed by hydrolysis of acetic anhydride (Equation 6) which is formed from methyl acetate and CO rather than by direct hydrolysis of methyl acetate. 

Activities of Group VIII Metal Catalysts. Methanol conversions to methyl acetate and acetic acid on group VIII metals supported upon activated carbon are illustrated in Figure 1, The yield was calculated as methanol conversion to acetyl group. For each catalyst, acetic acid formation is predominant at high temperature while methyl acetate has a point of maximum yield. 

Since copper (II) does not catalyze the AMP decomposition, the mechanism for acetic acid formation in the presence of copper (II) acetate is indicated by Reactions 17 and 18. 

While most of the above carbonylations are carried out at pressures greater than 40 atm (isocyanate and acetic acid formations are exceptions), decarbonylations are low pressure reactions. Decarbonylation of acyl halides catalyzed by (3P)2RhCOCl leads either to halides (65) (Reaction 19)... 

IV. Heat with dilute Sulphuric Acid.—Odour of formic acid, acetic acid—formates, acetates respectively. 

The conversion of methanol to ethanol with carbon monoxide and hydrogen has attracted considerable attention. Further carbonylation to higher alcohols occurs much more slowly, but acetic acid formation is a competing reaction and this leads to ester formation. Using CoI2 in presence of PBu 3 as catalyst, the selectivity to ethanol was improved by addition of the borate ion B4072. 399 This was attributed to an enhanced carbene-like nature of an intermediate cobalt-acyl complex by formation of a borate ester (equation 76). This would favour hydrogenolysis to... 

Scheme 8. Acetic acid formation from methane. Methane (5 atm), VO(acac)2 (0.05 mmol), l<2S208 (5 mmol), TFA (20 mL), 80°C, 20 h.

In heterogeneous system, Hattori et al.[63] observed a direct formation of acetic acid from H2/CO2 over Ag-Rh(0.2-l)/SiO2 catalyst at the condition of 2 Mpa, 20013, GHSV=12000 and H2/C02=l/2. Carbon monoxide was a main product with 96% selectivity, however, acetic acid was produced with 2.4% selectivity. They speculated that direct insertion of CO2 to surface methyl species on Rh led acetate formation, followed by hydrogenation to acetic acid. Acetic acid formation was ascribed to a... 

In homogeneous system, Fukuoka et al.[64] found acetic acid formation from H2/CO2 and CHsI using bimetalhc catalysts system such as Ru3(CO)i2 + Co2(CO)8 and Ni(cod)2+Co2(CO)8 in DMF solvent at the condition of 4 Mpa, ISOT , H2/C02=l/1 and 24h. Acetic acid was produced with 50% selectivity and by product was mainly CO. Their proposed reaction mechanism was composed of CO2 insertion to Ru-CHs species, followed by hydrogenation of its intermediate to acetic acid by HCo(CO)4. ... 

There are two possible pathways to homologate methanol with carbon dioxide the CO2 insertion path and CO insertion path (Scheme 2). As for the former, Fukuoka et al. reported that the cobalt-ruthenium or nickel bimetallic complex catalyzed acetic acid formation from methyl iodide, carbon dioxide and hydrogen, in which carbon dioxide inserted into the carbon-metal bond to form acetate complex [7]. However, the contribution of this path is rather small because no acetic acid or its derivatives are detected in this reaction. Besides, the time course... 

Acetic acid. Formation, synthetic acetic acid, glacial acetic acid. Aromatic... 

Evaluation of quantum yield of acetic acid formation at light intensity (L=254 nm) 1=1 TO quant/cm sec gives the value =().()2 close to the value of quantum yield of ester groups destruction (=0,015), measured in similar conditions [162]. Close value of quantum yield of acetic acid formation 0=0,01 has been obtained in the case of polyvinyl acetate photolysis at lower intensity - I=5,7T0 " quant/cm sec [163]. Data on effect of temperature on the rate of acetic formation are given in Table 1. Activation energy of the reaction of acetic acid formation at CA irradiation, calculated according to these results, is E,=9,66 kJ/mole, which is characteristic for photoprocesses. 

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