Diisobutylene formation

The fact that about five times as much of 2,3,4,4-tetramethyl-l-pentene (XXXVIII) was obtained as its 2-isomer (XXXIX) indicates that the loss of a proton from either of the two methyl groups takes place about five times as easily as do the loss of the proton on the tertiary carbon atom that is part of the neopentyl system. Similarly, the relative amounts of 3,5,5-trimethyl-2-hexene and its 3-isomer (XL and XLI) indicates that the loss of a proton from the ethyl group occurs about five times as readily as from the neopentyl group no loss of a proton from the methyl group appears to have occurred. By analogy with the formation of the two isomeric diisobutylenes from the ear-bonium ion VI it would be expected that the carbonium ion XLII which leads to the formation of 2,4,4-trimethyl-2-hexene (XLIII) would yield the 1-isomer in about four to five times the amount of the 2-isomer. The failure to find any of the 1-isomer was little less than startling (Whitmore and Mixon, 47). 

The formation of the other diisobutylene isomer is explained by assuming that isobutylene may also behave as H+ CH=r=C(CH3)2 ... 

In order to predict the formation of the isobutylene trimers, three alkenes may be considered to be activated, the original isobutylene and the two diisobutylenes. The various possibilities are shown in the following equations ... 

The reaction is run with excess ethylene to drive the equilibrium to product formation. The byproduct isobutylene is recycled to produce diisobutylene via dimerization (see Section 13.1.1). 

It seems certain that acid-catalyzed true oligomerization occurs via a carbocatio-nic mechanism as first suggested by Whitmore.5 Thus, the formation of diisobutylenes by dimerization of isobutylene in the presence of acidic catalysts occurs according to the following equation ... 

Fig. 24. Dependences of the initial rate of TBA formation and ratio of DIP/TBA on H3PMo,2O40 concentration in the hydration of butenes. TBA, lerl-butyl alcohol DIB, diisobutylene. 357 K, isobutylene/1-butene = 1/1 (molar). (From Ref. 163.)...

The chemical method for the measurement of interfacial area in liquid-liquid dispersions was first suggested by Nanda and Sharma (S19). They calculated the effective interfacial area a by sparingly extracting soluble esters of formic acid such as butyl formate, amyl formate, etc., into aqueous solutions of sodium hydroxide. This method has been employed by a number of workers, using esters of formic acid, chloroacetic acid, and oxalic acid, which are sparingly soluble in water (D9, DIO, FI, F2, F3, 04, P8, SI5, S20). Sankholkar and Sharma (S5) employed the extraction of diisobutylene into aqueous sulphuric acid. Sankholkar and Sharma (S6, S7) have also found that the extraction of isoamylene into aqueous solutions of sulphuric acid, and desorption of the same from the loaded acid solutions into inert hydrocarbons such as n-heptane and toluene, can be used for determining the effective interfacial area. Recently, Laddha and Sharma (L2) employed the extraction of pinenes into aqueous sulphuric acid. 

The temperature of the mixture should be kept in the range 20-25°. Higher temperatures lead to the formation of diisobutylene, and at lower temperatures (15°) the urea does not dissolve readily. Even at 25° the urea is usually not completely in solution. It has been found convenient to warm the feri.-butyl alcohol to about 30-35° before placing it in the dropping funnel. This avoids solidification in the stem (the melting point of tert.-hutyl alcohol is 25.5°). 

Chroman formation occurred in the reaction of 2-(2,2,4,4-tetramethyl)butylhydroquinone (from hydroquinone and diisobutylene) with... 

The convenient synthesis of a-hydroxyl-co-methoxycarbonyl asymmetric telechelic PIBs has been achieved by the combination of two recently discovered techniques, haloboration-initiation and end capping with 1,1-diphenylethylene followed by end quenching with silyl ketene acetals, 1 -methoxy-1 -trimethylsiloxy-2-methyl-propene (MTSMP), 1-methoxy-1-trimethylsiloxy-propene (MTSP), and 1-methoxy-l-trimethylsiloxy-ethene (MTSE). Nearly quantitative chain end functionalization has been proved by NMR, quantitative NMR, and FT-IR spectroscopy. The methoxycarhonyl end arising by quenching with MTSMP could not be hydrolyzed under either basic or acidic conditions. These methods also failed to yield the acid when the corresponding diisobutylene derivative was used. The sterically less hindered esters, however, readily underwent hydrolysis resulting in the formation of a-hydroxyl-co-carboxyl asymmetric telechelic PIBs. 

To produce p-tert-octylphenol, phenol and diisobutylene (a mixture of 2,4,4-trimethyl-l-pentene and 2,4,4-trimethyl-2-pentene) are fed through a bed of ion-exchange resin in the ratio 1.5 1 the resin is maintained at a temperature of 100 to 105 °C by internal cooling tubes. The alkylation is restricted to 95% diisobutylene conversion, to avoid the formation of undesirable by-products. The reaction mixture, which is separated into its constituents by vacuum distillation, consists of 93 to 96% p-tert-octylphenol the concentration of o-tert-octylphenol is between 2 and 3%. 

Also in non-cyclic, branched hydrocarbons cleavage of the carbon chain may occur under formation of carbonium ions, e. g. by depolymerization and disproportionation, as discussed in the previous chapter. Thus, under suitable reaction conditions diisobutylene may yield 2 moles of pivalic acid. Aside from cracking of C-C bonds, carbonium ions may also be obtained from paraffins by hydride transfer. 

---