Unsaturated Bonds, Reaction Maleic Anhydride with

Structopendant unsaturated polyesters, containing double bonds within the polymer chain, are produced by step-growth polycondensation reaction of an unsaturated diacid or anhydride, such as fumaric add or maleic anhydride, with a diol. Structural unsymmetry in the diol component lowers the viscosity of the prepolymer. Mostly, crosslinking of the structopendant unsaturated polyester is accomplished by copolymerization with alkene monomers such as styrene, methyl methacrylate, or others using radical initiators. 

Cyclopentadiene contains conjugated double bonds and an active methylene group and can thus undergo a Diels-Alder diene addition reaction with almost any unsaturated compound, eg, olefins, acetylene, maleic anhydride, etc. The number of its derivatives is extensive only the reactions and derivatives considered most important are discussed. 

The Diels-Alder reaction,is a cycloaddition reaction of a conjugated diene with a double or triple bond (the dienophile) it is one of the most important reactions in organic chemistry. For instance an electron-rich diene 1 reacts with an electron-poor dienophile 2 (e.g. an alkene bearing an electron-withdrawing substituent Z) to yield the unsaturated six-membered ring product 3. An illustrative example is the reaction of butadiene 1 with maleic anhydride 4 ... 

Maleic acid is a linear four carbon molecule with carboxylate groups on both ends and a double bond between the central carbon atoms. The anhydride of maleic acid is a cyclic molecule containing five atoms. Although the reactivity of maleic anhydride is similar to other cyclic anhydrides, the products of maleylation are much more unstable toward hydrolysis, and the site of unsaturation lends itself to additional side reactions. Acylation products of amino groups with maleic anhydride are stable at neutral pH and above, but they readily hydrolyze at acid pH values around pH 3.5 (Butler et al., 1967). Maleylation of sulfhydryls and the phe-nolate of tyrosine are even more sensitive to hydrolysis. Thus, maleic anhydride is an excellent reversible blocker of amino groups to temporarily mask them from reactivity while another... 

The uncatalyzed or uninitiated reaction takes place at higher temperatures, i.e. >160 °C. The reaction is not affected by radical trapping agents and is characterized by a low degree of gelation and essentially no loss of unsaturation. The structure of the adduct (179) is completely different and results from an ene reaction with maleic anhydride functioning as enophile (Scheme 86). Presence of the vinylidene double bond has been confirmed by IR and NMR spectroscopy. 

Reactive polymer processing has been used extensively in the manufacture of carboxyl-containing polymers (8). The carboxylation of unsaturated polymers with maleic anhydride (MAH) proceeds through the ene reaction where succinic anhydride is attached to the polymer with a shift of the double bond to the adjacent site. 

Af-Unsubstituted pyrazoles and indazoles add to compounds containing activated double and triple bonds (67HC 22)1,B-76MI40402>. Amongst C—C double and triple bonds, maleic anhydride, acrylic acid esters and nitriles, acetylene-carboxylic and -dicarboxylic esters (78AHC(23)263), quinones, and some a,/3-unsaturated ketones have been used with success. Phenylacetylene reacts with pyrazole in the presence of Na/HMPT as catalyst to yield the Z isomer of 1-styrylpyrazole in a highly stereoselective reaction (78JHC1543). 

Palladium-based catalysts also bring about cyclopropanations in high-yield. With palladium acetate/CHjNj, styrene , unactivated terminal olefins strained olefins , 1,3-dienesan enamine , as well as a,3-unsaturated carbonyl compounds have been cyclopropanated (Table 1). Contrary to an earlier report, the reaction also works well with cyclohexene if the conditions are chosen appropriately it seems that the notniyst is rapidly deactivated in the presence of this olefin >. Trisubstituted a,p-unsaturated carbonyl compounds were found to be unreactive, and the same is true for the double bonds in diethyl fumarate, maleic anhydride, coumarin and 1,3-dimethyluracil. Whereas the latter two were totally unreactive, [3-1-2] cycloaddition of diazomethane gave pyrazolines in the former two cases. The last entry of Table 1 shows that an allyl alcohol function can still be cyclopropanated, but methylene insertion into the O—H bond is a competing process. 

S-Unsaturated hydrazones such as (12) have been shown to behave as 1 -aza-1, 3-dienes in Diels-Alder addition reactions with a range of dienophiles such as maleic anhydride (Scheme 2). The dimethylamino substituent in the cycloadducts (e.g. 13) may be cleaved by treatment with zinc and acetic acid, but no conditions have so far been found to cleave the N-N bond without reducing the C-C double bond 5-Nitropyrimidine undergoes inverse Diels-Alder cycloaddition with electron-rich dienophiles such as enamines and ketene N,N- and 0,0-acetals (Scheme 3). ... 

In general, polyester resins are synthesized by the reaction between carboxylic acids and alcohols, with three or more reactive groups. Recently, unsaturated polyesters were incorporated in various ways to produce terminal, pendant, and internal double bonds [57-59]. In the case of unsaturated polyesters, maleic anhydride is most commonly used to produce internal unsaturation. The double bond present on unsaturated polyester reacts with a vinyl monomer, mainly styrene, resulting in a 3D crosslinked structure. This structure acts as a thermoset. The crosslinking is initiated through an exothermic reaction involving an organic peroxide, such as methyl ethyl ketone peroxide or benzoyl peroxide (Fig. 3.18). 

Maleic anhydride is unsaturated. Its reaction with diethylene glycol leads to a prepolymer with residual double bonds on the main chain. These participate in cross-linking reactions with styrene during initiation with benzoyl peroxide. The result is a network polymer. 

Besides the addition of halogens and hydrohalogens across the double bond just covered, there are many other reagents that will react similarly with unsaturated polymers by free radical, ionic, or radical-ion mechanisms. Of prime importance is the addition of ethylene derivatives to polydienes. One of the earliest reactions of natural rubber to be studied in detail was the combination with maleic anhydride (Cunneen and Porter, 1965). Depending on the reaction conditions and the presence or absence of free radical initiators, one or more of four basic reactions may take place, with the products shown (the arrows indicate where the addition has taken place and the new bonds formed). 

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