Acetals residue

Poly(vinyl alcohol) used to manufacture the poly(vinyl acetal)s is made from poly(vinyl acetate) homopolymer (see Vinyl polymers, vinyl alcohol polymers Vinyl POLYMERS, vinyl acetate polymers). Hydrolysis of poly(vinyl acetate) homopolymer produces a polyol with predominandy 1,3-glycol units. The polyol also contains up to 2 wt % 1,2-glycol units that come from head-to-head bonding during the polymeri2ation of vinyl acetate monomer. Poly(vinyl acetate) hydrolysis is seldom complete, and for some appHcations, not desired. For example, commercial PVF resins may contain up to 13 wt % unhydroly2ed poly(vinyl acetate). Residual vinyl acetate units on the polymer help improve resin solubiHty and processibiHty (15). On the other hand, the poly(vinyl alcohol) preferred for commercial PVB resins has less than 3 wt % residual poly(vinyl acetate) units on the polymer chain. 

Ethylene has also been copolymerised with a number of non-olefinic monomers and of the copolymers produced those with vinyl acetate have so far proved the most significant commercially . The presence of vinyl acetate residues in the chain reduces the polymer regularity and hence by the vinyl acetate content the amount of crystallinity may be controlled. Copolymers based on 45% vinyl acetate are rubbery and may be vulcanised with peroxides. They are commercially available (Levapren). Copolymers with about 30% vinyl acetate residues (Elvax-Du Pont) are flexible resins soluble in toluene and benezene at room temperature and with a tensile strength of about lOOOlbf/in (6.9 MPa) and a density of about 0.95 g/cm. Their main uses are as wax additives and as adhesive ingredients. 

Chloro-6-desoxy-3,5-benzylidene-l,4-anhydro-D-sorbitol (XVI) possesses an unusual property in that the benzylidene group is removed by distillation in alkaline or neutral solution. From the neutral solution it was possible to isolate 6-chloro-6-desoxy-l,4-anhydro-D-sorbitol as its triacetyl derivative. At the same time diacetyl-1,4 3,6-dianhydro-D-sorbitol was also formed. This removal of an acetal residue from a... 

Initially, the four acetate residues (Ri) are decarboxylated into methyl groups. The resulting coproporphyrInogen III returns to the mitochondria again. The subsequent steps are catalyzed by enzymes located either on or inside the inner mitochondrial membrane. 

Chlormadinone acetate is a synthetic progestagen used to prevent or suppress ovulation. Injection of chlormadinone acetate intramuscularly at a level of 200 mg in the neck of a veal calf results in relatively high residue concentrations in the urine of the treated animal (13). Levels of chlormadinone acetate residues in the urine of calves were found to range between 6 and 18 ppm. 

In sheep treated intravaginally with medroxyprogesterone acetate, residues were highest and more persistent in fat lower residue levels were found in liver and muscle. Mean residue concentrations in fat were higher than 20 ppb at 2 h posttreatment, declining to 14 ppb at 2 days and to approximately 7.5 ppb at 5 days posttreatment. Residues in liver and muscle were 2 ppb at 2 h and 1 ppb at 2 days posttreatment, respectively, declining to less than 1 ppb at 5 days posttreatment. In kidney, residue levels were less than 1 ppb at all time points. 

An exemplary investigation of the biosynthesis of multicolic acid by fungi (from acetate via phenolic intermediates) made full use of H NMR spectra with LIS shifts and I3C spectra obtained for substrates enriched by [1-13C]-, [2-13C]- and [l,2-13C]-acetate (79MI31006). The 13C chemical shifts are shown with structure (150) the lJ values for the heavy bonds show intact acetate residues and are 48 Hz for the single bond and 90 Hz for... 

SYNTHESIS A solution of 10.0 g 3-methoxy-4-ethoxybenzaldehyde in 150 mL nitromethane was treated with 1.7 g anhydrous ammonium acetate, and heated on the steam bath for 1 h. The excess nitromethane was removed under vacuum, yielding a loose, yellow crystalline mass that was filtered and modestly washed with cold MeOH. The 8.0 g of damp yellow crystals thus obtained were dissolved in 50 mL of vigorously boiling CH3CN, decanted from a small amount of insolubles (probably ammonium acetate residues) and cooled in an ice bath. The crystals so obtained were removed by filtration, washed with 2x5 mL cold CH3CN, and air dried to constant weight. The yield of 4-ethoxy-3-methoxy-B-nitrostyrene was 6.3 g of beautiful yellow crystals. 

LLE using 2.0 N HC1 and extracted with ethyl acetate. Residue reconstituted in mobile phase... 

A similar series of reactions for cevine (15) has been studied (49). However, the derived D-orthoacetate triacetate was shown to come into equilibrium with cevine tetraacetate in aqueous acetic acid. Although the tetraacetate was isolated and characterized, it is not known which of the three tertiary alcohol groups of ring D carried the fourth acetate residue. 

The next step was the introduction of the methylene acetal residue in 6 and 7 (Scheme 5). The initial plan was to effect this transformation in a single step, by exposure of the methoxymethyl derivatives 6 and 7 to dimethylboron bromide, following the conditions developed by Roush and co-workers (38). However, this reaction was not successful for either substrate, presumably due to competing cleavage of the acetonide residue. More promising results were obtained with triol 29 (obtainable from controlled hydrolysis of 7). Thus,... 

Treatment to Produce Starch Acetate Residuals Limitation... 

The greater the degree of NBS oxidation of the enzyme the slower was the rate with which its acetyl derivative parted with the acetate residue. The results are shown in Fig. 28. Interestingly enough the acetyl derivative of unoxidized chymotrypsin lost its acetate residue at a much slower rate than the rate of appearance of maximum enzymatic activity. The half-time of deacetylation was about 3 min, whereas maximal activity with the acetylchymotrypsin was obtained about 1.0-1.5 min after its addition to substrate at pH 8.0. 

The ground drug was extracted with ethanol. Distillation of the alcohol afforded a residue which was dissolved in diluted sulfuric acid. After separation of undissolved materials by filtration and extraction of non-basic products with ligroin the solution was made alkaline. First the solution was extracted exhaustively with ether and then with ethyl acetate. An oily residue was obtained from the ether solution and a solid one from the ethyl acetate solution. The ether-soluble oily fraction, dissolved in 2-propanol, yielded mesembrine hydrochloride upon acidification with ethereal hydrochloric acid. Fractional crystallization of the concentrated mother liquors gave, besides some mesembrine hydrochloride, the hydrochloride of mesembrenine. Crystallization of the solid ethyl acetate residue from a mixture of ethyl acetate and 2-propanol afforded channaine. 

Analysis of the CH correlation signals (CH COSY/CH COLOC) for the protons at 7.38 and 5.54ppm (Table 40.1) shows this ring to be a five-membered lactone. The CH correlation signals with the protons at 4.65ppm (AB system of methylene protons on C-10) and 2.04ppm (methyl group) identify and locate an acetate residue (CO ... 

Esters are much less sensitive than ketones to Zn(BH4)2 or cyanoborohydrides [PSl], and the selective reduction of the ketone groups of a- and P-ketoesters can be accomplished without problems (Section 3.2.4). Moreover, Zn(BH4)2 in DME under sonication reduces acetates or cyclohexanecarboxylates while benzoates are left untouched [R3]. The chemoselective reduction of the acetate residue of 3.163 can be performed under these conditions (Figure 3.55). 

The atoms of the acetate residue are in the general 48-fold positions. The acidic H atoms lie on twofold axes in special positions of multiplicity... 

The NH4 ion and the dimeric ZHZ of the first set are sited on crystallographic centres of symmetry. (A centre of symmetry is, of course, impossible for the tetrahedral NH4 ion, which must be disordered in this case.) In the second set, the NH4, X and HZ are in general positions, duplicated by operation of crystallographic centres of inversion. Thus the crystal contains both Type A and Type B structure NH4HZ2 and 2 (NH4Z. HZ) respectively. The structural plan, as it affects the acetate residues, is represented schematically by Fig. 10. 

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