Unsaturated, from vinyl

The second largest use at 21% is for unsaturated polyester resins, which are the products of polycondensation reactions between molar equivalents of certain dicarboxyhc acids or thek anhydrides and glycols. One component, usually the diacid or anhydride, must be unsaturated. A vinyl monomer, usually styrene, is a diluent which later serves to fully cross-link the unsaturated portion of the polycondensate when a catalyst, usually a peroxide, is added. The diacids or anhydrides are usually phthahc anhydride, isophthahc acid, and maleic anhydride. Maleic anhydride provides the unsaturated bonds. The exact composition is adjusted to obtain the requked performance. Resins based on phthahc anhydride are used in boat hulls, tubs and spas, constmction, and synthetic marble surfaces. In most cases, the resins contain mineral or glass fibers that provide the requked stmctural strength. The market for the resins tends to be cychcal because products made from them sell far better in good economic times (see Polyesters,unsaturated). 

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

Vinyl plastics Group of plastics composed of resins derived from vinyl monomers, excluding those that are covered by other classifications (i.e., acrylics and styrene plastics). Examples include PVC, poly(vinyl acetate), poly(vinyl butyral), and various copolymers of vinyl monomers with unsaturated compounds. 

The fact that the cyclization is directed to an acetylenic group and leads to formation of an alkenyl radical is significant. Formation of a saturated iodide would be expected to lead to a more complex product mixture because the cyclized product could undergo iodine abstraction and proceed to add to a second unsaturated center. Vinyl iodides are much less reactive, and the reaction product is stable to iodine-atom abstraction. Because of the potential for competition from reduction by the stannane, other reaction conditions have been developed to promote cyclization. Hexabutylditin is frequently used.238... 

Anomolous results have been observed in some emulsion polymerizations—inverse dependencies of N, Rp, and Xn on surfactant concentration. Some surfactants act as inhibitors or retarders of polymerization, especially of the more highly reactive radicals from vinyl acetate and vinyl chloride [Okamura and Motoyama, 1962 Stryker et al., 1967]. This is most apparent with surfactants possessing unsaturation (e.g., certain fatty acid soaps). Degradative chain transfer through allyl hydrogens is probably quite extensive. 

The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyI-7-lactone 419[380]. The /3,7-unsaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

Palladium acetate triarylphosphine complexes catalyze the addition of vinylic groups from vinylic halides to olefinic compounds in the presence of amines. Conjugated dienes are major products from 0,/3-unsaturated acids, esters, or nitriles while unactivated olefinic compounds react best in the presence of secondary amines where allylic amines are major products. The reactions are usually regio- and stereospecific. The synthetic utility of the reaction is illustrated with a wide variety of examples. 

As a second example, there is a wide variety of breakdown products and oligomeric products that may be formed from the reactive monomers that are the building blocks of plastics. For plastics, the general assumption has been that any side-reaction products and breakdown products are likely to be significantly less toxic than the monomers, and so restricting the migration of the monomer was accepted as an indirect way to limit any hazard from the oligomers also. Whilst this approach is probably acceptable for addition polymers, such as those made from the unsaturated monomers vinyl chloride, butadiene and acrylonitrile where the unsaturated monomer is far more noxious than their products, the validity of this means of indirect control is questionable for condensation polymers such as polyesters and for polyethers formed from epoxide monomers. 

The chroniium(VI) oxide-dipyridine complex also has beoi found to cause oxidative rearrangement of tertiary allylic alcohols to a,3-epoxy aldehydes and small amounts of a,3-unsaturated aldehydes (equation 6 and Table 3). This is potentially useful as a homologation sequence since the starting materials are readily available from vinyl metal addition to ketones. Use of pyridinium chlorochromate (PCC) for this transformation gives mosdy a,3 unsaturated aldehydes. 

A general method for the synthesis of a,/8-unsaturated aldehydes from vinyl-silanes has been incorporated into a new synthetic route to ( )-nuciferal (102) (Scheme 9). ... 

Conjugate addition reaction is also promoted by superbases. Novikov et al. reported that the intramolecular Michael addition of a,p-unsaturated ester 31, which was obtained from vinyl diazoacetate in the presence of rhodium acetate [Rh2(OAc)4], proceeded with DBU to give the spirocyclic indole skeleton 32 in 90% yield [7] (Scheme 7.5). This strucmre can be seen in intriguing, complex natural products, such as marcfortines 33 and 34. 

Unsaturated polyester resins are generally reinforced with glass fibers and have many applications, from transparent building construction elements to boat hulls. Their application is facilitated by the use of what are known as SMCs (sheet molding compounds). SMCs are formulated mixtures of unsaturated polyesters, vinyl monomers, initiators, and glass fibers supplied as a sandwich between two poly (ethylene) films. To apply, one film is removed, and the resin layer is pressed onto the mold with rollers, and thus... 

The basic reaction is a radical polymerisation starting from vinyl monomers, i.e., unsaturated molecules of form R — CH = CH2, where R is a substituent which may itself be unsaturated. The monomers may be introduced singly to produce homopolymers, but more commonly, they are used in mixtures for the preparation of copolymers. Monomer molecules are highly sensitive to the presence of free radicals R these primary radicals initiate chain reactions which add monomer units, following the classic scheme... 

This is a more reactive form of unsaturation than vinyl, and is used extensively in free radical curing formulations, where the extra reactivity is of benefit, e.g., acrylics, some polyesters. Commercial products usually contain y-methacryloxy propyl groups, and hence the double bond is further away from the silicon than is the case with the vinyl silane. As mentioned previously, Jang and co-workers have studied the effect of the length of the spacer group [69]. 

Bromobenzene and benzyl chloride also afforded ester, but chlorobenzene did not give the desired product. The reaction is applicable for the synthesis of a,/3-unsaturated ester from vinyl halide, and it is tolerant of a variety of functional groups, cis- and trans-Vinyl hahdes were carbobutoxylated for retaining the initial stereochemistry in the product (Table 2). 

Vinyl iodonium salt 40, which is highly effective as an activated species of vinyl iodide, could be synthesized from vinyl silanes 39 by the reaction with iodosyl benzene and triethyloxonium tetrafluoroborate. Thus, from vinyl silane, a,/3-unsaturated ester 41 could be synthesized by Pd-catalyzed carbonylation (Eq. 12). Alkynylphenyliodo-nium tosylates 42 were easily prepared from 1-alkynes with Phl(OH)OTs or by reaction... 

---