3- Hydroxyisobutyric acid/3-Hydroxyisobutyrate

Selected physical properties of various methacrylate esters, amides, and derivatives are given in Tables 1—4. Tables 3 and 4 describe more commercially available methacrylic acid derivatives. A2eotrope data for MMA are shown in Table 5 (8). The solubiUty of MMA in water at 25°C is 1.5%. Water solubiUty of longer alkyl methacrylates ranges from slight to insoluble. Some functionalized esters such as 2-dimethylaniinoethyl methacrylate are miscible and/or hydrolyze. The solubiUty of 2-hydroxypropyl methacrylate in water at 25°C is 13%. Vapor—Hquid equiUbrium (VLE) data have been pubHshed on methanol, methyl methacrylate, and methacrylic acid pairs (9), as have solubiUty data for this ternary system (10). VLE data are also available for methyl methacrylate, methacrylic acid, methyl a-hydroxyisobutyrate, methanol, and water, which are the critical components obtained in the commercially important acetone cyanohydrin route to methyl methacrylate (11). 

The reaction is mn for several hours at temperatures typically below 100°C under a pressure of carbon monoxide to minimise formamide decomposition (73). Conversions of a-hydroxyisobutyramide are near 65% with selectivities to methyl a-hydroxyisobutyrate and formamide in excess of 99%. It is this step that is responsible for the elimination of the acid sludge stream characteristic of the conventional H2SO4—ACH processes. Because methyl formate, and not methanol, is used as the methylating agent, formamide is the co-product instead of ammonium sulfate. Formamide can be dehydrated to recover HCN for recycle to ACH generation. 

The methyl a-hydroxyisobutyrate produced is dehydrated to MMA and water in two stages. First, the methyl a-hydroxyisobutyrate is vaporized and passed over a modified zeoHte catalyst at ca 240°C. A second reactor containing phosphoric acid is operated at ca 150°C to promote esterification of any methacrylic acid (MAA) formed in the first reactor (74,75). Methanol is co-fed to improve selectivity in each stage. Conversions of methyl a-hydroxyisobutyrate are greater than 99%, with selectivities to MMA near 96%. The reactor effluent is extracted with water to remove methanol and yield cmde MMA. This process has not yet been used on a commercial scale. 

Hydroxy-2-methylpropionic acid (a-hydroxyisobutyric acid, 2-methyllactic acid)) [594-6I-6J M 104.1, m 79 , b 114 /12mm, 212 /760mm, pK 3.78. Distd in steam, crystd from diethyl ether or benzene, sublimed at 50° and dried under vacuum. 

The first methacrylic esters were prepared by dehydration of hydroxyisobutyric esters, prohibitively expensive starting points for commercial synthesis. In 1932 J. W. C. Crawford discovered a new route to the monomer using cheap and readily available chemicals—acetone, hydrocyanic acid, methanol and sulphuric acid— and it is his process which has been used, with minor modifications, throughout the world. Sheet poly(methyl methacrylate) became prominent during World War II for aircraft glazing, a use predicted by Hill in his early patents, and since then has found other applications in many fields. 

The adjacent iodine and lactone groupings in 16 constitute the structural prerequisite, or retron, for the iodolactonization transform.15 It was anticipated that the action of iodine on unsaturated carboxylic acid 17 would induce iodolactonization16 to give iodo-lactone 16. The cis C20-C21 double bond in 17 provides a convenient opportunity for molecular simplification. In the synthetic direction, a Wittig reaction17 between the nonstabilized phosphorous ylide derived from 19 and aldehyde 18 could result in the formation of cis alkene 17. Enantiomerically pure (/ )-citronellic acid (20) and (+)-/ -hydroxyisobutyric acid (11) are readily available sources of chirality that could be converted in a straightforward manner into optically active building blocks 18 and 19, respectively. 

The synthesis of intermediate 19 commences with aldehyde 33 (see Scheme 5b), a substance readily available in enantiomerically pure form from (+)-/ -hydroxyisobutyric acid (11)20. Exposure of... 

C4H9NO2 13027-88-8) see Dimethadione D(-)-3-bydroxyisobutyric acid (C4HSO3 1910-47-0) see Captopril a-hydroxyisobutyric acid (C4H,03 594-61-6) see Dimethadione... 

Kemp and Waters also found the oxidations of cyclohexanone and of mandelic, malonic and a-hydroxyisobutyric acids by Cr(VI) to be Mn(II)-catalysed. In these cases, as with oxalic acid, the [Cr(VI)] versus time plots are almost linear and the reaction becomes first order in substrate (or involves Michaelis-Menten kinetics), and, except at lowest catalyst concentrations, approximately first order in [Mn(II)]. Detailed examination of the initial rate of oxidation of a-hydroxyrobutyric acid as a function of oxidant concentration revealed, however, that the dependence is... 

C-C fission to give IV for both V(V) and Mn(III). Kemp and Waters have established two main features of these oxidations, namely, (i) for the oxidations of QH5CD(0H)C02H and the light compound are V(V), 2.0 Mn(III) sulphate, 1.2 Ce(lV) sulphate, 1.1 and (i7), that the trend of rates of oxidation of mandelic, a-hydroxyisobutyric, lactic and glycollic acids is as expected for Ce(IV) and Mn(III) if stabilisation of the radical RCHOH is important, but is altered for V(V) (Fig. 4). It appears from the latter observations that the presence of a-hydrogen atoms causes a drop in rate by a factor of almost 10 per a-hydrogen... 

Nuryono, Huber, C. G., and Kleboth, K., Ion-exchange chromatography with an oxalic acid-alpha-hydroxyisobutyric acid eluent for the separation and quantitation of rare-earth elements in monazite and xenotime, Chromatograph-ia, 48, 407, 1998. 

Hydroxycarbonic adds, such as dtric, tartaric, malic, and hydroxyisobutyric acid, but also gluconate or glucoheptonate, are assumed to form the same kind of complex as the polyols do [23,28,29]. 

Several methods have been used to separate the lanthanides chemically solvent extraction, ion exchange chromatography, HPLC using Q-hydroxyisobutyric acid and, in limited cases, selective reduction of a particular metal cation.40-43 The use of di(2-ethylhexyl)orthophosphoric acid (HDEHP) for the separation of various rare-earth elements via solvent extraction has also been reported.44 16 This separation method is based on the strong tendency of Ln3+ ions to form complexes with various anions (i.e., Cl- or N03 ) and their wide range of affinities for com-plexation to dialkyl orthophosphoric acid. When the HDEHP is attached to a solid phase resin, the lanthanides can be selected with various concentrations of acid in order of size, with the smallest ion being the most highly retained. 

The need to achieve high yield in one-pot synthesis, coupled to the relative kinetic inertness of rhenium complex (e.g. compared to technetium) and the mild conditions required has led to the development of useful versatile rhenium(V) intermediates that can be quickly prepared in quantitative yield, and are metastable, i.e. kinetically labile enough to react rapidly with the final chelator, again in high yield. The most widely used ligands suitable for this purpose are polydentate hydroxycarboxylic acids such as glucoheptonate [116a], citrate (47), tartrate (48), and 2-hydroxyisobutyric acid (49) [159]. Examples are discussed elsewhere in this chapter. They are typically used in the presence of Sn(II) to reduce Re(VII) to Re(V), at moderately elevated temperature (50-100 °C) at pH 2-3 (acid pH promotes reduction of perrhenate, presumably by facilitat-... 

The ACH process has recently been improved, as stated by Mitsubishi Gas. Acetone-cyanohydrin is first hydrolized to 2-hydroxyisobutylamide with an Mn02 catalyst the amide is then reacted with methylformiate to produce the methyl ester of 2-hydroxyisobutyric acid, with coproduction of formamide (this reaction is catalyzed by Na methoxide). The ester is finally dehydrated with an Na-Y zeolite to methylmethacrylate. Formamide is converted to cyanhydric acid, which is used to produce acetone-cyanohydrin by reaction with acetone. The process is very elegant, since it avoids the coproduction of ammonium bisulphate, and there is no net income of HCN. Problems may derive from the many synthetic steps involved, and from the high energy consumption. 

The enthalpies and entropies of formation of mono-mandelato-complexes have been determined and, in comparison with other hydroxycarboxylic acid complexes, the enthalpy order of stabilization is lactate > a-hydroxyiso-butyrate mandelate > glycolate, whereas the entropy order of stabilization is glycolate > a-hydroxyisobutyrate > mandelate > lactate. The stability constants and enthalpy of formation of mono- and di-malonate complexes have also been measured.The mono-1,1-cyclopentanedicarboxylato-complexes are less stable than the corresponding malonate species. 

Paramethadione Paramethadione, 5-ethyl-3,5-dimethyloxazolidine-2,4-dione (9.8.3), differs from trimethadione only in the substitution of one methyl group with an ethyl gronp. It is synthesized in a completely analogons manner, except that it comes from 2-hydroxy-2-methylbntyric acid instead of 2-hydroxyisobutyric acid [29]. 

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