Vinyl ester exchange

Chemistry. Poly(vinyl acetate) can be converted to poly(vinyl alcohol) by transesterification, hydrolysis, or aminolysis. Industrially, the most important reaction is that of transesterification, where a small amount of acid or base is added in catalytic amounts to promote the ester exchange. 

Uses Plasticizer for lacquers, plastics, cellulose esters, and vinyl resins heat-exchange liquid carbonless copy paper systems in aircraft hydraulic fluids solvent extraction of metal ions from solution of reactor products uranium extraction and nuclear fuel reprocessing pigment grinding assistant antifoaming agent solvent for nitrocellulose and cellulose acetate. 

The next step in the reaction sequence must involve attack of acetate or chloride to give the Pd (II) a-bonded carbon intermediate. First consider the case of acetate using vinyl ester exchange as an example. If acetate were attacking from the coordination sphere, it must enter the coordination sphere by means of the equilibrium shown in Equation 12. What would the rate expression for this route be First the equilibria shown in Equation 10 would require a [Li2Pd2Cl6] [C2H3OOCR]/[LiCl] term in the rate expression while Equation 12 would require a [LiOAc] / [LiCl] term so the complete rate expression would be that given by Equation 13. Actually the rate expression contained a [LiCl] term to the first power,... 

The allyl propionate exchange (Equation 4) also involves acetoxy-palladation, and thus its kinetic behavior might be expected to parallel that for vinyl propionate exchange. In its general features it is, in fact, very similar to vinyl ester exchange. The rate profile with sodium acetate concentration is of the same form as Figure 1. 

Poly(vinyl acetate), PVAc, of molecular weights (M ) 6.1x1 01, 1.9xl05, and 6.0xl05, was randomly labeled by ester exchange with 2,2,5,5-tetramethyl-3-pyrrolin-l-oxyl-3-carboxylic acid to give a spin labeled polymer containing typically 1-10 nitroxides per polymer molecule. Polystyrene was prepared by emulsion... 

The complete polymer may now be attacked by reagents that cleave the ester groups. Water is a possibility, but methanol penetrates the polymer better and ester exchange in alkaline solution gives poly(vinyl alcohol). 

Furthermore, a study of vinyl ester exchange, which proceeds by a mechanism analogous to the acetoxypalladation mechanism for olefin oxidation [see Section III, B, 1, Eqs. (174) and (175)], indicates that the dimer is the most catalytically active species, with the trimer next, and the monomer, (NaaPd(OAc)4), unreactive. In the study of Moiseev et ah, a maximum rate is attained at the point at which the concentration of Na2Pd2(OAc)g reaches a maximum. Thus the dimer is the reactive species rather than Na2Pd(OAc)4. However, the decrease in rate with increasing [NaOAc] is greater than can be explained on the basis of conversion of dimer to unreactive monomer [Eq. (5), Section II, A, 2]. 

It is interesting to compare this tentative rate expression with that found for vinyl ester exchange [Section III, B, 1, Eq. (173)] which does not contain the [NaOAc] inhibition term because of a cancellation of the inhibition term with a catalytic term in [NaOAc], The rate-determining step for the vinyl ester exchange is the acetoxypalladation step. The added term in the oxidation rate expression suggests that acetoxypalladation is not the slow step but rather the decomposition of the acetoxypalladation adduct. Furthermore, the decomposition must be inhibited by acetate. The following scheme is consistent with other Pd(II) as well as Pt(II) chemistry ... 

The vinyl ester exchange has also been studied in the chloride-free palladium(II) acetate system, using vinyl propionate as substrate. Of the three Pd(II) species present in this system (Section II, A, 2), the dimer is most reactive, with the trimer Pd3(OAc)g next, and the monomer unreac-tive. The rate expression for exchange catalyzed by the dimer is (214). 

Scheme 4.4 details a short synthesis by Trost of an intermediate employed in the Gerlach synthesis of 9. ° Protected aldol 19 was reacted with a-lithio ethyl vinyl ether and the resulting alkoxide intermediate acylated to provide the protected diol 20 in 75% yield. Chain extension by way of a palladium-mediated allylic displacement with isopropyl phenylsulfonylacetate followed by ester exchange afforded a 62% yield of 21. Hydrolysis of the enol ether and 3-elimination of the sulfonyl group produced 22 in 66% yield. Ketalization of 22 then gave 16, which had been previously converted to the natural product in 50% yield. 1 ... 

This is a kinetic resolution that works by enantioselective acylation of the unwanted enantiomer of the alcohol. The reaction is therefore an ester exchange and vinyl acetate is an efficient acetate transfer agent since the other product is vinyl alcohol better known as the enol of acetaldehyde so the reaction is irreversible. 

The vinyl monomer of CyD is synthesized by the ester exchange reaction of m-nitrophenyl acrylate with (3-CyD or a-CyD in water. The imprinted polymers are prepared in water by a conventional radical co-polymerization of the vinyl monomer of CyD with N,N,-methyl-enebisacrylamide (MBAA) as crosslinker in the presence of various templates acryloyl CyD (300 pmol) and template (150 pmol) are dissolved in 15 mL of Tris buffer solution ([Tris] = 5 mM, pH 8.0). After stirring for a few minutes, the polymerization is started by adding MBAA (3.0 mmol) and potassium persulfate (35 mg) under nitrogen at 50 °C. The system becomes opaque as the polymerization proceeds. After stirring for 2 h, the obtained white precipitate is collected and... 

Phenylmenthol 116 was used as a chiral auxiliary for the synthesis of (-)-triptolide. Ester exchange of 115 with 116 in the presence of DMAP provided the acyclic precursor 117. Cyclization of 117 afforded the major diasteriomer 118. Vinyl triflate 119 was reduced... 

This is a classic Claisen [3,3]-sigmatropic rearrangement sequence starting with an allylic alcohol and forming a vinyl ether by acetal (or in this case ortho ester) exchange. The reaction is very trans selective. 

Among polymerization catalysts, Ziegler catalysts (EtsAl and TiCLt), Natta catalysts (EtsAl and TiCT), and metallocene catalysts (Cp2M(Ti, Zr, Hf, Fe) and -(O-Al(R))n-(R=Me, Ft)) are used as vinyl polymerization catalysts. Ca, Hg, Zn, and Cd compounds and Ti, Ge, Sn, Pb, and Sb compounds are used for ester exchange and their polyester polymerization catalysts, respectively. 

Aromatic crystalline polyesters, including PET, PBT, poly(ethylene naphthalene) (PEN) and poly(trimethylene terephthalate) (PTT), are typically considered to be engineering polymers, thus many of the examples of aromatic polyester blends will be discussed in Section 4.6. Polyesters exhibit the ability of ester exchange in blends with structurally different polyesters, leading to block copolymer formation during thermal exposure. With hydroxyl containing polymers, such as the polyhydroxyether of Bisphenol A (Phenoxy PHE) and poly(4-vinyl... 

Recently, several other aminopolymers were synthesized for the NCA polymerization. Ichie and coworkers used copolymers of styrene-vinyl benzylamine and methyl methacrylate-vinyl benzylamine for NCA polymerization to study the kinetics of NCA polymerization with macroinitiators. 2 The polymerization was Ist-order with respect to monomer concentration and was much faster in nitrobenzene than in dioxane or THF. Kiba patented a new system for NCA polymerization with the different aminopolymers [38] produced according to Scheme 5. He also claimed the ester exchange reaction of the resulting graft copolymer with ethylene cyanohydrin over p-toluene sulfonic acid. 

Substitution at the Carbon—Chlorine Bond. Vinyl chloride is generally considered inert to nucleophilic replacement compared to other alkyl halides. However, the chlorine atom can be exchanged under nucleophilic conditions in the presence of palladium [7440-05-3] Pd, and certain other metal chlorides and salts. Vinyl alcoholates, esters, and ethers can be readily produced from these reactions. 

A variety of waxy hydrophobic hydrocarbon-based soHd phases are used including fatty acid amides and sulfonamides, hydrocarbon waxes such as montan wax [8002-53-7], and soHd fatty acids and esters. The amides are particularly important commercially. One example is the use of ethylenediamine distearamide [110-30-5] as a component of latex paint and paper pulp blackHquor defoamer (11). Hydrocarbon-based polymers are also used as the soHd components of antifoaming compositions (5) examples include polyethylene [9002-88-4], poly(vinyl chloride) [9002-86-2], and polymeric ion-exchange resins. 

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