Ester groups group ratios

Titanoxanes can also be prepared by reaction of a tetraalkyl titanate and carboxyUc acids (25). If the ratio of carboxyUc acid to tetraalkyl titanate is 1 1, a simple polymeric titanate ester is formed. If two or more moles of acid are used per mole of tetraalkyl titanate, the resulting polymeric titanate ester contains ester carboxylate groups. 

The most successful of these products contain high ratios of VP to DMAEMA and are partially quatemized with diethyl sulfate (Polyquaternium 11) (142—144). They afford very hard, clear, lustrous, nonflaking films on the hair that are easily removed by shampooing. More recendy, copolymers with methyl vinyl imidazoliiim chloride (Polyquaternium 16) (145) or MAPTAC (methacrylamidopropyltrimethyl ammonium chloride) (Polyquaternium 28) have been introduced. Replacement of the ester group in DMAEMA with an amide analog as in Polyquaternium 28 results in a resin resistant to alkaline hydrolysis and hence greater utility in alkaline permanent-wave and bleach formulations (see Quaternary ammonium compounds). 

The acetylation reaction is stopped by the addition of water to destroy the excess anhydride, causing rapid hydrolysis of the combined sulfate acid ester (Eig. 7). This is followed by a much slower rate of hydrolysis of the acetyl ester groups. The rate of hydrolysis is controlled by temperature, catalyst concentration, and, to a lesser extent, by the amount of water. Higher temperatures and catalyst concentrations increase the rate of hydrolysis. Higher water content slightly iacreases the hydrolysis rate and helps minimize degradation (85). The amount of water also influences the ratio of primary to secondary... 

AplP ratio. The Ap/ P ratio is calculated by dividing the numbers of carbon atoms in aliphatic chains in a plasticizer molecule by the number of ester groups present. The Ap/P ratio correlates well with several properties of the plasticizers such as melting point, density, modulus and water absorption. 

Acid anhydrides have been employed with, and without the use of a base catalyst. For example, acetates, propionates, butyrates, and their mixed esters, DS of 1 to ca. 3, have been obtained by reaction of activated cellulose with the corresponding anhydride, or two anhydrides, starting with the one with the smaller volume. In all cases, the distribution of both ester groups was almost statistic. Activation has been carried out by partial solvent distillation, and later by heat activation, under reduced pressure, of the native cellulose (bagasse, sisal), or the mercerized one (cotton linters). No catalyst has been employed the anhydride/AGU ratio was stoichiometric for microcrystalhne cellulose. Alternatively, 50% excess of anhydride (relative to targeted DS) has been employed for fibrous celluloses. In all cases, polymer degradation was minimum, and functionalization occurs preferentially at Ce ( C NMR spectroscopic analysis [52,56,57]). 

The crucial cyclization of 129 was accomplished by oxidation with pyri-dinium chlorochromate (PCC) and acetylation, providing two cyclohexane derivatives (130 and 131) in the ratio of 10 1. Thermal decarboxylation of 130 resulted in formation of the cyclohexene derivative 132, with concomitant elimination. Reduction of the ester group with diisobutylaluminum hydride converted 132 into 133. Hydroboration-oxidation of 133 gave the carba-sugar derivative 134 as a single product. 

Influence of the Monovalent Ions. The addition of ammonium salts retard the course of the deesterification by changing the reaction rate of hydrolysis and ammonolysis. By increasing the concentration of the ions the conversion of the ester groups is reduced from 83.3 % for 0,01 M to 62.8 % for 0.2 M (without added salt this value is 84.05 %), and the ratio hydrolysis ammonolysis is changed correspondingly from 53.8 76.2 to 37.3 62.7 (without added salt this ratio is 57.6 42.4). 

Clavepictines A and B (210 and 211, respectively) were obtained from the allenic ester 227. The reduction of its ester group to aldehyde, followed of addition to the latter of hexylmagnesium bromide, OH protection, and N-deprotection gave compound 228. A silver(i)-mediated cyclization of this compound afforded quinolizidine 229 and its C-6 epimer in a 7 1 ratio (Scheme 44). The former compound was readily converted into the target alkaloids <1997JOC4550>. 

ABNP is soluble in dimethylformamide (DMF) but insoluble directly in aqueous solution. Insulin labeling was done in DMF water at a ratio of 9 1. For molecules not soluble in organic solvent, such as proteins, the trifunctional first may be dissolved in DMF and a small aliquot added to an aqueous reaction medium. The nitrophenyl ester reactive group can be coupled to amine groups at alkaline pFI (7-9) and in buffers containing no extraneous amines (avoid Tris). Unfortunately, ABNP is not commercially available at the time of this writing. 

Amongst the first studies presenting the use of dendritic polymers for thermoset applications was the work of Hult et al. [62]. They modified hyperbranched hydroxy functional polyesters with various ratios of maleate-allyl ether/alkyl ester end groups. Dependent on this ratio, resins with different vis-... 

Cationic chiral Rh2 carboxamidates show catalytic activity for the DCR between diaryl nitrones and methacrolein (Scheme 11). Cycloadducts were obtained as 3,4-endo/3,5-endo mixtures with molar ratios ranging from 13/87 to 90/10. The enantioselectivity of the 3,4 isomers is higher than that of the 3,5 adducts and increases when the steric bulk of the ligand ester group increases [36]. 

For the unsubstituted compound 197a-Me the 2R/2S ratio was only 5.6 1 [ 10b, c], yet in this case the absolute configuration was checked by X-ray crystal structure analysis. The a-azidoesters 197-R were converted to the a,)3-diamino acids 198-R as described above, i.e. by catalytic hydrogenation over palladium on charcoal and hydrolysis of the ester group (Scheme 58) [10b, c, 62]. Saponification was not necessary for the benzyl esters 197a,b,i-Bn. 

The percentage of diester, keto-ester and diketone end groups in the copolymers depends on the relative rates of alcoholysis and protonolysis. For example, when these two termination processes occur at a comparable rate, the diester, keto-ester and diketone end groups are in a 1 2 1 ratio, respectively [11], The use of oxidant co-reagents may increase the amount of ester end groups [lb], while the chain-transfer mechanism controls the nature of the termination metal product (Pd-OR, Pd-OH and Pd-H). 

As before, p is the fraction of functional groups that have already reacted (see Eq. 4.1), i.e., the mols of ester groups formed (Nq and N are the numbers of functional groups present at the start and a given time of the reaction, respectively), (1 -p) the molar quantity of unreacted hydroxy and carboxy groups, and is the mole fraction of water present in the reaction mixture. Solving Eq. 4.5 for p we obtain the upper limit of conversion as a function of the ratio p = Klriy -. 

In transition state TS2, leading to the minor perepoxide intermediate PE2 in a limiting step, the oxygen is placed syn to the ester group, and the net dipole moment is expected to be larger than that in transition state TSi where the oxygen has an anti orientation with respect to the ester group. TS2 is therefore more polar than TSi, and expected to be stabilized better by polar solvents than TS]. Consequently, the ratio 79a/79b decreases with increase of solvent polarity. 

The combination of the geometrical preference of the tether and the stereochemical preference of the dipolarophile substituent can be seen in the intramolecular cycloadditions of alkyl nitronates, (Scheme 2.6) (99). When the tether is restricted to two atoms, only the endo approach of the tether is observed in up to a 100 1 ratio, independent of the configuration of the disubstituted dipolarophile. However, in the case of a three-atom linker, there exists a matched and mismatched case with respect to the observed stereoselectivities. With a (Z)-configured dipolarophile, only the exo isomer was observed since the ester moiety also approaches on the exo to the nitronate. However, with an ( )-configured dipolarophile, the ester group is forced to approach in an endo manner to accommodate an exo approach of the tether, thus leading to lower selectivity. 

---