Pentenes 2,2,4-trimethyl-1-pentene

The intramolecular oxidative earbonylation has wide synthetie applieation. The 7-lactone 247 is prepared by intramolecular oxycarbonylation of the alke-nediol 244 with a stoichiometric amount of Pd(OAc)2 under atmospheric pres-sure[223]. The intermediate 245 is formed by oxypalladation, and subsequent CO insertion gives the acylpalladium 246. The oxycarbonylation of alkenols and alkanediols can be carried out with a catalytic amount of PdCl2 and a stoichiometric amount of CuCb, and has been applied to the synthesis of frenolicin(224] and frendicin B (249) from 248[225]. The carbonylation of the 4-penten-l,3-diol 250, catalyzed by PdCl2 and CuCl2, afforded in the c -3-hydroxytetrahydrofuran-2-aeetie acid lactone 251[226J. The cyclic acetal 253 is prepared from the dienone 252 in the presence of trimethyl orthoformate as an accepter of water formed by the oxidative reaction[227]. 

Together these two products contain all eight carbons of the starting alkene The two carbonyl carbons correspond to those that were doubly bonded m the original alkene One of the doubly bonded carbons therefore bears two methyl substituents the other bears a hydrogen and a tert butyl group The alkene is identified as 2 4 4 trimethyl 2 pentene (CH3)2C=CHC(CH3)3 as shown m Figure 6 15... 

The same reaction that gave 2 4 4 trimethyl 2 pentene also yielded an isomeric alkene This second alkene produced formaldehyde and 4 4 dimethyl 2 pentanone on ozonolysis Identify this alkene... 

FIGURE6 15 Ozonolysis of 2 4 4 trimethyl 2 pentene On cleavage each of the doubly bonded carbons becomes the carbon of a carbonyl (C=0) group... 

Step 3 Loss of a proton from this carbocation can produce either 2 4 4 trimethyl 1 pentene or 2 4 4 trimethyl 2 pentene... 

Esters. The monoisobutyrate ester of 2,2,4-trimethyl-1,3-pentanediol is prepared from isobutyraldehyde ia a Tishchenko reaction (58,59). Diesters, such as trimethylpentane dipelargonate (2,2,4-trimethylpentane 1,3-dinonanoate), are prepared by the reaction of 2 mol of the monocarboxyhc acid with 1 mol of the glycol at 150—200°C (60,61). The lower aUphatic carboxyHc acid diesters of trimethylpentanediol undergo pyrolysis to the corresponding ester of 2,2,4-trimethyl-3-penten-l-ol (62). These unsaturated esters reportedly can be epoxidized by peroxyacetic acid (63). 

Mesityl Oxide. Mesityl oxide (MSO) (4-metliyl-3-penten-2-one) is an oily colorless liquid with an unpleasant odor. It exhibits the versatiUty and unusual reactivity associated with conjugated a,P unsaturated carbonyl compounds (172). On standing ia air, mesityl oxide slowly forms bis(3,5,5-trimethyl-l,2-dioxolanyl)-3-peroxide (173). 

Since a carbocation can add to an alkene to form a larger cation, under acidic conditions isobutylene can dimerize to form 2,4,4-trim ethyl -1 -pen ten e [107-39-1] and 2,4,4-trimethyl-2-pentene [107-40-4J, which can then be hydrogenated in the presence of nickel to form isooctane [540-84-1]. This reaction is no longer of commercial significance. 

Chemical Designations - Synonyms 2,4,4-Trimethyl-l-pentene Chemical Formula ... 

When high purity isobutylene is not required, the acid extract from the rich stage may be heated for a few minutes to 250-300°F, and then quickly cooled. Under these conditions the isobutylene dimerizes to form largely 2,4,4, trimethyl pentene-1. This is known as the dimer process and may be used to concentrate i-butenes for dehydrogenation feed, the isobutylene dimer being added to the motor gasoline pool. Trimers, as well as codimers with normal butenes are also produced. 

The same reaction that gave 2,4,4-trimethyl-2-pentene also... 

The two dimers of (CH3)2C=CH2 are formed by the mechanism shown in Figure 6.16. In step 1 protonation of the double bond generates a small amount of tert-butyl cation in equilibrium with the alkene. The car bocation is an electrophile and attacks a second molecule of 2-methylpropene in step 2, forming a new carbon-carbon bond and generating a carbocation. This new carbocation loses a proton in step 3 to form a mixture of 2,4,4-trimethyl-l-pentene and 2,4,4-trimethyl-2-pentene. 

This process produces polymer gasoline with a high octane. Dimerization was first used (1935) to dimerize isobutylene to diisobutylene, constituted of 2,4,4-trimethyl-1-pentene (80%) and 2,4,4-trimethyl-2-pentene (20%). Both phosphoric and sulfuric acid were used as catalysts. 

Two approaches for the synthesis of allyl(alkyl)- and allyl(aryl)tin halides are thermolysis of halo(alkyl)tin ethers derived from tertiary homoallylic alcohols, and transmetalation of other allylstannanes. For example, dibutyl(-2-propenyl)tin chloride has been prepared by healing dibutyl(di-2-propenyl)stannane with dibutyltin dichloride42, and by thermolysis of mixtures of 2,3-dimethyl-5-hexen-3-ol or 2-methyl-4-penten-2-ol and tetrabutyl-l,3-dichlorodistannox-ane39. Alternatively dibutyltin dichloride and (dibutyl)(dimethoxy)tin were mixed to provide (dibutyl)(methoxy)tin chloride which was heated with 2,2,3-trimethyl-5-hexen-3-ol40. 

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