Isobutylene, reaction with acids

Substituted Phenols. Phenol itself is used in the largest volume, but substituted phenols are used for specialty resins (Table 2). Substituted phenols are typically alkylated phenols made from phenol and a corresponding a-olefin with acid catalysts (13). Acidic catalysis is frequendy in the form of an ion-exchange resin (lER) and the reaction proceeds preferentially in the para position. For example, in the production of /-butylphenol using isobutylene, the product is >95% para-substituted. The incorporation of alkyl phenols into the resin reduces reactivity, hardness, cross-link density, and color formation, but increases solubiHty in nonpolar solvents, dexibiHty, and compatibiHty with natural oils. 

Methylphenol is converted to 6-/ f2 -butyl-2-methylphenol [2219-82-1] by alkylation with isobutylene under aluminum catalysis. A number of phenoHc anti-oxidants used to stabilize mbber and plastics against thermal oxidative degradation are based on this compound. The condensation of 6-/ f2 -butyl-2-methylphenol with formaldehyde yields 4,4 -methylenebis(2-methyl-6-/ f2 butylphenol) [96-65-17, reaction with sulfur dichloride yields 4,4 -thiobis(2-methyl-6-/ f2 butylphenol) [96-66-2] and reaction with methyl acrylate under base catalysis yields the corresponding hydrocinnamate. Transesterification of the hydrocinnamate with triethylene glycol yields triethylene glycol-bis[3-(3-/ f2 -butyl-5-methyl-4-hydroxyphenyl)propionate] [36443-68-2] (39). 2-Methylphenol is also a component of cresyHc acids, blends of phenol, cresols, and xylenols. CresyHc acids are used as solvents in a number of coating appHcations (see Table 3). 

Ritter Reaction (Method 4). A small but important class of amines are manufactured by the Ritter reaction. These are the amines in which the nitrogen atom is adjacent to a tertiary alkyl group. In the Ritter reaction a substituted olefin such as isobutylene reacts with hydrogen cyanide under acidic conditions (12). The resulting formamide is then hydroly2ed to the parent primary amine. Typically sulfuric acid is used in this transformation of an olefin to an amine. Stoichiometric quantities of sulfate salts are produced along with the desired amine. 

Sulfuric acid is about one thousand times more reactive with isobutylene than with the 1- and 2-butenes, and is thereby very useful in separating isobutylene as tert-huty alcohol from the other butenes. The reaction is simply carried out by bubbling or stirring the butylenes into 45—60% H2SO4. This results in the formation of tert-huty hydrogen sulfate. Dilution with water followed by heat hydrolyzes the sulfate to form tert-huty alcohol and sulfuric acid. The Markovnikov addition implies that isobutyl alcohol is not formed. The hydration of butylenes is most important for isobutylene, either directiy or via the butyl hydrogen sulfate. 

Separation and Purification of Isomers. 1-Butene and isobutylene caimot be economically separated into pure components by conventional distHlation because they are close boiling isomers (see Table 1 and Eig. 1). 2-Butene can be separated from the other two isomers by simple distHlation. There are four types of separation methods avaHable (/) selective removal of isobutylene by polymeriza tion and separation of 1-butene (2) use of addition reactions with alcohol, acids, or water to selectively produce pure isobutylene and 1-butene (3) selective extraction of isobutylene with a Hquid solvent, usuaHy an acid and (4) physical separation of isobutylene from 1-butene by absorbents. The first two methods take advantage of the reactivity of isobutylene. Eor example, isobutylene reacts about 1000 times faster than 1-butene. Some 1-butene also reacts and gets separated with isobutylene, but recovery of high purity is possible. The choice of a particular method depends on the product slate requirements of the manufacturer. In any case, 2-butene is first separated from the other two isomers by simple distHlation. 

I eopentanoic (Pivalic) Acid. Neopentanoic acid [75-98-9] is prepared using the Koch technology in which isobutylene reacts with carbon monoxide in the presence of strong acids such as H2SO4, HF, and BF H20 (119—122). General reaction conditions are 2—10 MPa (about 20—100 atm) of CO and 40-150°C. 

Isobutylene oxide is produced in a way similar to propylene oxide and butylene oxide by a chlorohydrination route followed by reaction with Ca(OH)2. Direct catalytic liquid-phase oxidation using stoichiometric amounts of thallium acetate catalyst in aqueous acetic acid solution has been reported. An isobutylene oxide yield of 82% could be obtained. 

Studies of hydrosilation with trichlorosilane-d (2f) proved that exchange can also take place between SiD and C—H bonds in olefins during hydrosilation. Isobutylene was chosen as the olefin for this study because both it and isobutyltrichlorosilane have H NMR spectra that are easy to interpret, and because movement of the double bond can give rise to no detectable isomerization. Excess trichlorosilane-d with isobutylene and chloroplatinic acid was sealed into a Pyrex tube and kept near 25°C overnight. Deuterosilation was complete in less than 1 hour. Analysis of the product after about 16 hours indicated reactions that can be summed up as follows ... 

The crucial step in self-alkylation is decomposition of the butoxy group into a free Brpnsted acid site and isobutylene (proton transfer from the Fbutyl cation to the zeolite). Isobutylene will react with another t-butyl cation to form an isooctyl cation. At the same time, a feed alkene repeats the initiation step to form a secondary alkyl cation, which after accepting a hydride gives the Fbutyl cation and an -alkane. The overall reaction with a linear alkene CnH2n as the feed is summarized in reaction (10) ... 

Table III provides a comparison of alkylate compositions for both the liquid acid-catalyzed reactions with various feed alkenes. The data show that H2SO4 produces a better alkylate with 1-butene, whereas HF gives better results with propene or isobutylene. The products from 2-butene and also from pentenes (not shown in Table III) are nearly the same with either acid.

The reaction of isobutylene with 91% sulfuric acid at 0° yielded a product which contained 63% of paraffin in the fraction boiling below 200° when 87% sulfuric acid was used only traces of paraffins were found in the corresponding fraction, while with 77 % acid no paraffins at all were produced. No polymerization of isobutylene occurred with 67% acid at 0° at 35°, on the other hand, polymer composed of di- and triisobutylene was obtained. 

Water, alcohols, ethers, or amines can cause inhibition of ionic polymerization. However, these substances can act in different ways according to their concentration. For example, in polymerizations initiated by Lewis acids (BF3 with isobutylene) or organometallic compounds (aluminum alkyls), water in small concentrations behaves as a cocatalyst, but in larger concentrations as an inhibitor (reaction with the initiator or with the ionic propagating species). 

The mechanism most consistent with all the data is an ionic acid opening of the epoxide —apparently where the hydrocarbonyl is used as an acid to attack the epoxide— which is more sensitive to steric effects than to electronic factors. This conclusion may at first appear to be inconsistent with our previous finding that isobutylene reacted with cobalt hydrocarbonyl to give exclusively addition of the cobalt to the tertiary position. The inhibitory effect of carbon monoxide on that reaction, however, indicated that it was probably cobalt hydrotricarbonyl that was actually adding to the olefin and steric effects would be expected to be much less important with the tricarbonyl than with the tetracarbonyl (7) Apparently he feels now that the former reactions really involve the tricarbonyl, loss of CO being important to get the reaction running whereas epoxide attack perhaps involves a tetracarbonyl, steric factors are more important here. 

Formation of C8 alkanes in the alkylation of isobutane even when it reacts with propene or pentenes is explained by the ready formation of isobutylene in the systems (by olefin oligomerization-cleavage reaction) (Scheme 5.2). Hydrogen transfer converting an alkane to an alkene is also a side reaction of acid-catalyzed alkylations. Isobutylene thus formed may participate in alkylation Cg alkanes, therefore, are formed via the isobutylene-isobutane alkylation. 

The direction of ring opening of nnsymmetnea) episulfides by thiols in the presence of either acid or base catalyst appears to be rather non-selective.1 Mixtures of primary and tertiary mercaptan have been obtained by reaction of isobutylene Bulfido with some of the simple aliphatic thiols such as -butanethiol in the presence of catalytic quantities of either boron trifluoride or sodium ethoxide (Eq. 43). 

Figure 3 describes the preparation of A-co-undecenoyl-L-valine CSP bonded to silica gel. The carboxylic acid group of L-valine was protected by the reaction with isobutylene using the method of Roeske [47]. The formed tert-butyl ester of L-valine was precipitated from diethyl ether as the oxalate by the dropwise addition of a solution of 10% oxalic acid in absolute ethanol. The precipitate is dried and the oxalate group is removed by the reaction of sodium hydroxide. The tert-butyl ester of L-valine was treated with undecenoic acid in tetrahydrofuran (THF), which resulted in A-co-undecenoyl-L-valine methyl ester. In another step, lOmM of monochlorosilane was dissolved in 20 mL of dry pyridine and was allowed to react with /V -to - u ndccenoyl-L-valine methyl ester. 

Isobutylene is present as 20-30% of the C4 fraction from the naphtha cracking process. A number of different upgrading reactions with isobutylene have been carried out industrially (with and without prior separation from the C4 fraction). One of these includes the acid-catalyzed oligomerization... 

More than 20 runs were made to Investigate the reaction between Isobutane and the products of first-effect reactions with Isobutylene. Alkylate was not produced until excess acid was used and larger amounts of excess acid were needed for runs at -30°C as compared to runs at -10 c (3). An acld-to-olefin ratio of about 1.0 was required at -10 C to obtain TMP s whereas a 7 1 ratio was needed at -30 C. 

The alkylation mechanism for second-step reactions with isobutylene as the olefin have been significantly clarified by two runs, each conducted as follows. The acid and hydrocarbon phases produced by first-step reactions involving Isobutylene and sulfuric acid were separated. The acid phase which contained some acid-soluble hydrocarbons or reaction products such as perhaps t-butyl sulfate was then contacted with fresh Isobutane. This resulting mixture of reactants was designated as A below. The hydrocarbon... 

The Importance of Reaction 1-2 has not yet been proved however, some as yet unidentified acid-soluble hydrocarbons (formed from Isobutylene) react with Isobutane to form alkylate (6). 

Transfer of two hydride ions and one proton would result in DMH. Since the methyl groups could migrate on the chain, DMH s other than 2,5-DMH could be produced. Some t-butyl cations dissociate into isobutylene and protons hence this method could occur during alkylation with olefins other than isobutylene. Reaction N is probably only of minor Importance in most cases, however, since only small concentrations of free isobutylene are thought to occur at the acid-hydrocarbon interface most isobutylene quickly protonates to form t-butyl cations. 

It can be seen from Table 3 that AS values referring to ester hydrolysis are in the range —2 to +15 eu (entropy units = cal. degree-1 ) if the mechanism is Al, or in the range —15 to —30 eu if the mechanism is A2. However, if other reactions are included the Al and A2 ranges overlap. For the acid catalyzed hydrolyses of ethylene and isobutylene oxides, the AS values are —6 and —4 eu [49], respectively. The mechanism is some form of A2 in both cases (see Sect. 6.3). On the other hand, AS = —3.8 eu has been found for the acid catalyzed hydrolysis of 2,4,4,5,5,-pentamethyl-l,3-dioxolane [51], which may be an example of an Al reaction or possibly an A2+ reaction with strong steric hindrance (see Sect. 7.4). 

Several acids have been esterified by reaction with propene, " isobutylene, and ttimethylethylene. " The reaction is reversible and catalyzed by sulfuric acid or boron trifluoride. The optimum conditions for maximum conversion are low reaction temperature, large quantity of catalyst, and anhydrous conditions. " By this method, the keto ester, t-butyl o-benzoyl benzoate, " and the halo esters, f-butyl and isopropyl trichloroacetates,have been prepared. 

Several processes are used to upgrade the C4 fraction. The isobutydene contained in the C4 cut is removed by reaction with methanol to produce MTBE. The remaining n-butenes in the C4 cut can be alkylated with isobutane catalyzed by liquid HE or H2SO4 or isomcrized into isobutylene in the presence of acid catalysts. 

Allyl-/-butyltrithiocarbonates (236), which are obtained from readily available allyl halides by a multi-step reaction with sodium t-butyltrithiocarbonates, can be cyclized with concomitant loss of hydrogen iodide and isobutylene using elemental iodine to afford 1,3-dithiolane-2-thiones (237) ( heme 48) treatment of (237) with pyridine again results in a loss of hydrogen iodide and (238) is formed. Compound (238) can be isomerized using trifluoroacetic acid and (239) is obtained <80JOC2959>. 

Lewis acids are seldom effective sdone rather they require the presence of trace amounts of water or some other proton donor (protogen) such as hydrogen halide, alcohol, and carboxylic acid, or a carbocation donor (cationogen) such as t-butyl chloride or triphenylmethyl chloride, which, on reaction with the Lewis acid, forms the electrophilic species that initiates polymerization. Thus dry isobutylene is unaffected by dry boron trifluoride but polymerization occurs immediately when trace amounts of water are added. The initiation process for boron trifluoride and water is... 

By retro synthetic analysis collagenase inhibitor RO0319790 (1) can be assembled from two chiral building blocks, (R) -succinate 2 and (S)-tert-leucine N-methyla-mide 13. As the latter can be prepared from commercially available (S)-tert-leucine 8 our work concentrated in particular on the construction of the first building block 2. In order to assemble the carbon skeleton of 2 in the most efficient way, extremely cheap maleic anhydride 4 was converted in a known ene reaction with isobutylene to provide the cyclic anhydride 6. Hydrogenation of the double bond followed by the addition of EtOH/p-TsOH yielded the racemic diethyl ester substrate 9 for the enzyme reaction. The enzymatic monohydrolysis of 9 afforded the monoacid (R)-2a. (R)-2 a was coupled via its acid chloride with leucine amide 13 to ester 14, which finally was converted into the hydroxamic acid 1. 

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