2- -isobutyric acid

Isobutyric acid, dimethylacetic acid, 2-methylpropanoic acid, (CHjjjCH COOH, colourless syrupy liquid with an unpleasant odour b.p. 154°C. Prepared by oxidation of 2-methylpropanol with K2Cr207 and H2SO4. Salts soluble in water. Used in alkaline solution for sweetening gasoline. 

In the same chromatographic analysis for low-molecular-weight acids considered in Example 12.2, the retention time for isobutyric acid is 5.98 min. What is the selectivity factor for isobutyric acid and butyric acid ... 

First we must calculate the capacity factor for isobutyric acid. Using the void time from Example 12.2, this is... 

Dehydrogenation of Propionates. Oxidative dehydrogenation of propionates to acrylates employing vapor-phase reactions at high temperatures (400—700°C) and short contact times is possible. Although selective catalysts for the oxidative dehydrogenation of isobutyric acid to methacrylic acid have been developed in recent years (see Methacrylic ACID AND DERIVATIVES) and a route to methacrylic acid from propylene to isobutyric acid is under pilot-plant development in Europe, this route to acrylates is not presentiy of commercial interest because of the combination of low selectivity, high raw material costs, and purification difficulties. 

Carbocations generated from alkanes using superacids react with carbon monoxide under mild conditions to form carboxyUc acid (188). In this process isomeric carboxyUc acids are produced as a mixture. However, when the reaction is mn with catalytic amounts of bromine (0.3 mmol eq) in HF-SbF solution, regio-selective carboxylation is obtained. / -Propane was converted almost exclusively to isobutyric acid under these conditions. 

Propylene-Based Routes. The strong acid-catalyzed carbonylation of propylene [115-07-1] to isobutyric acid (Koch reaction) followed by oxidative dehydration to methacrylic acid has been extensively studied since the 1960s. The principal side reaction in the Koch reaction is the formation of oligomers of propylene. Increasing yields of methacrylic acid in the oxydehydration step is the current focus of research. Isobutyric acid may also be obtained via the oxidation of isobutyraldehyde, which is available from the hydroformylation of propylene. The -butyraldehyde isomer that is formed in the hydroformylation must be separated. 

The oxidative dehydration of isobutyric acid [79-31-2] to methacrylic acid is most often carried out over iron—phosphoms or molybdenum—phosphoms based catalysts similar to those used in the oxidation of methacrolein to methacrylic acid. Conversions in excess of 95% and selectivity to methacrylic acid of 75—85% have been attained, resulting in single-pass yields of nearly 80%. The use of cesium-, copper-, and vanadium-doped catalysts are reported to be beneficial (96), as is the use of cesium in conjunction with quinoline (97). Generally the iron—phosphoms catalysts require temperatures in the vicinity of 400°C, in contrast to the molybdenum-based catalysts that exhibit comparable reactivity at 300°C (98). 

The distikative separation of methacrylic acid from unreacted isobutyric acid is problematic because the boiling points of isobutyric acid (155°C) and methacrylic acid (162°C) are quite close to one another. Alternatively, the cmde reaction mixture can be esterified, and the resultant methyl methacrylate (101°C) and methyl isobutyrate (92°C) can be separated. 

Although not commercialized, both Elf Atochem and Rn hm GmbH have pubUshed on development of hydrogen fluoride-catalyzed processes. Norsolor, since acquired by Elf Aquitaine, had been granted an exclusive European Hcense for the propylene-hydrogen fluoride technology of Ashland Oil (99). Rn hm has patented a process for the production of isobutyric acid in 98% yield via the isomerization of isopropyl formate in the presence of carbon monoxide and hydrofluoric acid (100). 

Thus, -butyl [71-36-3] [71-36-3] and isobutyl alcohol [78-83-1] [78-83-1] are obtained by hydrogenation of their respective aldehydes and butyric and isobutyric acid are produced by oxidation. 

Catalytic oxidation of isobutyraldehyde with air at 30—50°C gives isobutyric acid [79-31-2] ia 95% yield (5). Certain enzymes, such as horseradish peroxidase, cataly2e the reaction of isobutyraldehyde with molecular oxygen to form triplet-state acetone and formic acid with simultaneous chemiluminescence (6). 

Isobutyraldehyde also undergoes consecutive aldol and Tischenko condensations to give 2,2,4-trimethyl-l,3-pentanediolmonoisobutyrate [25265-77-4] (Texanol, Filmer IBT), alternatively prepared by the esterification of TMPD with isobutyric acid. 

About 69% of the total 1988 U.S. consumption of isobutyraldehyde, went into the production of isobutyl alcohol and isobutyraldehyde condensation and esterification products. The other principal isobutyraldehyde derivative markets (as a percentage of total 1988 U.S. isobutyraldehyde consumption) are neopentyl glycol (15%) isobutyl acetate (6%) isobutyric acid (5%) isobutyUdene diurea (2.5%) and methyl isoamyl ketone (1.7%). 

The monoisobutyrate ester of TMPD, Texanol, or Filmer IBT, formally an isobutyraldehyde trimer, is prepared in a single step from isobutyraldehyde or, alternatively, by the esterification of TMPD with isobutyric acid. This monoester is most commonly employed as a coalescing agent for latex-based paints and water-based ink formulations. 

Isobutyric acid, the simple oxidation product of isobutyraldehyde, is employed in the esterification of TMPD to form the mono- and diesters of TMPD. Some isobutyric acid is also used in the production of isobutyronittile, an organo-phosphate pesticide precursor. 

Butyric acid is made by air-oxidation of butyraldehyde, which is obtained by appHcation of the oxo synthesis to propylene. Isobutyric acid is made from isobutyraldehyde, a significant product in the synthesis of butyraldehyde (see Butyraldehydes). Butyraldehyde is also used to make 2-ethylhexanoic acid. 

Clofibrate, shown to be an effective Upid lowering dmg in the eady 1960s, is the ethyl ester of/ -chlotophenoxy isobutyric acid. Gemfibrozil is a stmctural congener of clofibrate. 

Mevalonic acid 5-phosphate [1189-94-2] M 228.1, pKes,(d 1.5 (PO4H2), pKEst(2) 4.4 (CO2H), pKEst(3) (P04H ). Purified by conversion to the tricyclohexylammonium salt (m 154-156°) by treatment with cyclohexylamine. Crystd from water/acetone at -15°. Alternatively, the phosphate was chromatographed by ion-exchange or paper (Whatman No 1) in a system isobutyric acid/ammonia/water (66 3 30 Rp 0.42). Stored as the cyclohexylammonium salt. 

Aceton-losung, /. acetone solution. ><51, n. acetone oil. -saure, /. acetonic (o-hydrozy-isobutyric) acid. 

Iso-bare, /. isobar, -bernsteinsaure, /. iso-succinic acid, -buttersaure, /. isobutyric acid, -chinolin, n. isoquinoline. 

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