Other hydrolyses

Aryl carbazates (140) containing a methyl group in the 2-position hydrolyse by a BA( 2 mechanism but die others hydrolyse by an ElcB mechanism.119 This conclusion was reached from a study of a wide range of ring-substituted compounds. 

The total monosaccharide composition of OCL acid posthydrolysate is approx 26 g/L of monosaccharides, with a ratio of 2 5 3 for glucose xylose arabinose. Compared to other hydrolysates, it has higher arabinose but lower xylose contents than rice straw (37), sugarcane bagasse (38), Eucalyptus wood (16), and corncobs (36), where the latter two hydrolysates were also obtained in a similar two-step procedure. Nevertheless, the total monosaccharide content is in the same range, e.g., as rice straw, Eucalyptus wood, or corncobs. 

Although other researchers have reported the use of detoxification steps for other hydrolysates to be utilized by yeast (5,7,38,41), considering the low level of inhibitors present in the BSG OCL acid posthydrolysate, no special detoxification treatment was carried out, except adjustment of the hydrolysate pH to 5.5. For pH adjustment of the hydrolysate, several alkalis were tested, namely NaOH, CaO and Ca(OH)2. CaO, induced high foam... 

Other hydrolyses with sodium hydroxide have been described as follows. 2-Benzyloxy-6-chloropyrazine in ethanol with 3.5N sodium hydroxide at reflux for 4.5 hours gave 2-chloro-6-hydroxypyrazine (832), 2-chloro-6-metho)Qrpyrazine with aqueous ethanolic sodium hydroxide gave 2-chloro-6-hydroxypyrazine (43%) possibly containing a small amount of 2-hydroxy-6-methoxypyrazine) (883), and 2,6-dimethoxypyrazine with aqueous ethanolic sodium hydroxide at reflux for 24 hours formed 2-hydroxy-6-methoxypyrazine (832). 

Hydrolysis of the gums was often accompanied by the formation of a small amount of flufiy precipitate. Several gums that initially dissolved completely to give crystal clear solutions produced more of this brown residue than did gums that lacked clarity and ready solubility. These precipitates are denatured proteins or tannins often detected in plant gums. In two cases, those of Anogeissus latifolia and Astragalus gum-mifer, the hydrolysis was insufficient to cleave the more stable portions of the molecule. Those portions which were initially insoluble remained so but retained a white color quite different from the dark residue found in some other hydrolyses. Decomposition by the pathway shown previously was found to be less than 1% in every case tested. 

The study of a number of other hydrolyses by both tracer and stereochemical methods has shown that cleavage between oxygen and the acyl group is the usual one in ester hydrolysis. This behavior indicates that the preferred point of nucleophilic attack is the carbonyl carbon rather than the alkyl carbon this is, of course, what we might have expected in view of the generally greater reactivity of carbonyl carbon (Sec. 20.5). 

Cold aqueous N sodium hydroxide gave similar results, except that a 2-methyl group did not interfere with the hydrolysis. The alkaline ring opening of 6,9-dimethyl-8-azapurine stopped at 4-formamido-3-methyl-1,2,3-triazol-5-yl methyl ketone. This result indicated that the first stage in the reaction is 30. Similar 4-formamido-5-formytriazoles were isolated at an early stage in several of the other hydrolyses. 

Bismuth is the only metal forming a coloured complex with DDTC, in ammonia solutions, in the presence of EDTA and KCN, at pH 9-11. The Hg(DDTC)2 complex, also extractable under these conditions, does not absorb at 400 nm. Some tartrate should be added, if Al, Ti, or other hydrolysable elements are present. 

High-molecular-weight esters, such as wax esters, steryl esters, triterpenoid esters and triacylglycerols, are often hydrolysed, after which the liberated moieties are GC analysed however, this procedure provides only limited compositional information. The very convenient one-pot small-scale hydrolysis-silylation procedure, applicable to ester-emulsifiers, oils, fats, wax esters and other hydrolysable lipids, has been proposed by the lUPAC (Briischweiler and Hautfeune, 1990). The procedure involves the saponification of esters (ca. 10 mg) in 0.5 N ethanolic KOH solution (0.25 mL) at 80 °C for 3 h, evaporation to dryness in a stream of nitrogen and then silylation of the hydrolysis products. This enables the components of very small samples to be determined (< 0.1 mg). This procedure was used for the hydrolysis of wax esters and triterpenoid esters in potato and eggplant cuticular waxes (Szafranek Synak, 2006 Halinski et al., 2009). A solution of 1-2% (v/v) concentrated sulphuric acid in methanol can be easily used for the transesterification of acyl lipids and the esterification of free fatty acids (Christie, 1994). More procedures for ester hydrolysis and transesterification and for fatty acid esterification are described in detail by Christie (1994). 

Nifrilases catalyze the conversion of organonitriles directly to the corresponding carboxylic acids. Synthetic hydrolysis of nitriles into the corresponding amides and carboxylic acids requires severe reaction conditions. A typical synthetic approach would require the use of 70% H2SO4 and heat (13). Such a reaction condition is not compatible when selectivity and the conservation of other hydrolysable functional groups in a substrate are desired. Biotransformation of nitrites can be accomplished under mild conditions, in an aqueous environment (13). Additionally, enantioselectivity of the biocatalytic conversion of nitriles to chiral acids has been demonstrated (14-16). Therefore, nifrilases provide an alternative route for synthetic processes that require conversion of nitriles to corresponding acids. 

Van der Ven, V., Gruppen, H., de Bont, D. B. A., Voragen, A. G. J. (2001). Emulsion properties of casein and whey protein hydrolysates and the relation with other hydrolysate characteristics. Journal of Agricultural and Food Chemistry, 49, 5005-5012. 

Several other hydrolyses have been performed, although only products of low enantiomeric purity were obtained [494]. 

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