Butyl alcohols intermediates

These common features suggest that carbocations are key intermediates m alcohol dehydra tions just as they are m the reaction of alcohols with hydrogen halides Figure 5 6 portrays a three step mechanism for the acid catalyzed dehydration of tert butyl alcohol Steps 1 and 2 describe the generation of tert butyl cation by a process similar to that which led to its for matron as an intermediate m the reaction of tert butyl alcohol with hydrogen chloride... 

IS reversible with respect to reactants and products so each tiny increment of progress along the reaction coordinate is reversible Once we know the mechanism for the for ward phase of a particular reaction we also know what the intermediates and transition states must be for the reverse In particular the three step mechanism for the acid catalyzed hydration of 2 methylpropene m Figure 6 9 is the reverse of that for the acid catalyzed dehydration of tert butyl alcohol m Figure 5 6... 

Propylene oxide [75-56-9] (methyloxirane, 1,2-epoxypropane) is a significant organic chemical used primarily as a reaction intermediate for production of polyether polyols, propylene glycol, alkanolamines (qv), glycol ethers, and many other useful products (see Glycols). Propylene oxide was first prepared in 1861 by Oser and first polymerized by Levene and Walti in 1927 (1). Propylene oxide is manufactured by two basic processes the traditional chlorohydrin process (see Chlorohydrins) and the hydroperoxide process, where either / fZ-butanol (see Butyl alcohols) or styrene (qv) is a co-product. Research continues in an effort to develop a direct oxidation process to be used commercially. 

Synthesis. Titanium alkoxy halides are intermediates in the preparation of alkoxides from a titanium tetrahaUde (except the fluoride) and an alcohol or phenol. If TiCl is heated with excess primary alcohol, only two chlorine atoms can be replaced and the product is dialkoxydichlorotitanium alcoholate, (RO)2TiCl2 ROH. The yields are poor, and some alcohols, such as aHyl, ben2yl, and /-butyl alcohols, are converted to chlorides (46). Using excess TiCl at 0°C, the trichloride ROTiCl is obtained nearly quantitatively, even from sec- and / f/-alcohols (47,48). 

Alternatively, the intermediate acetaldehyde (qv) for this process was obtained from ethylene by the Wacker process (9). A small amount of -butyl alcohol is produced in the United States by the Ziegler-Natta chain growth reaction from ethylene [74-85-1] (10). 

Because of limitations on the ready availability of HCN, particularly in Japan, processes involving the oxidation of C4 intermediates have been developed and are now replacing the older route developed by Crawford. One important process is based on the two-stage oxidation of isobutylene or -butyl alcohol to methacrylic acid, which is then separated and esterified Figure 15.5a). 

As we have just seen, the rate-determining intermediate in the reaction of tert-butyl alcohol with hydrogen chloride is the carbocation (CH3)3C. Convincing evidence from a variety of sources tells us that carbocations can exist, but are relatively unstable. When carbocations are involved in chemical reactions, it is as reactive intermediates, formed slowly in one step and consumed rapidly in the next one. 

O-isopropylidene derivative (57) must exist in pyridine solution in a conformation which favors anhydro-ring formation rather than elimination. Considerable degradation occurred when the 5-iodo derivative (63) was treated with silver fluoride in pyridine (36). The products, which were isolated in small yield, were identified as thymine and l-[2-(5-methylfuryl)]-thymine (65). This same compound (65) was formed in high yield when the 5 -mesylate 64 was treated with potassium tert-hx Xy -ate in dimethyl sulfoxide (16). The formation of 65 from 63 or 64 clearly involves the rearrangement of an intermediate 2, 4 -diene. In a different approach to the problem of introducing terminal unsaturation into pento-furanoid nucleosides, Robins and co-workers (32,37) have employed mild base catalyzed E2 elimination reactions. Thus, treatment of the 5 -tosylate (59) with potassium tert-butylate in tert-butyl alcohol afforded a high yield of the 4 -ene (60) (37). This reaction may proceed via the 2,5 ... 

The cyclization of aryl 3-chloropropyl sulfones by potassium t-butoxide in t-butyl alcohol at 30 °C (equation 20) has a p value of 2.32 for substituents in Ar202. This is considered by Bird and Stirling to indicate the formation of an intermediate carbanion which is essentially in equilibrium with the reactants. A recent review by Stirling203 deals with structure-reactivity aspects of many sulfonyl promoted reactions of this type. 

The steric outcome in the above cyclization can be explained on the basis of either a zwitterionic intermediate or a concerted [7t2s -I- 7t2s] process , depending on the nature of the reactants . Definite predictions are practically impossible as yet. The more stable trans-isomers (i.e. 221a) can be obtained by stirring the isomeric mixture with catalytic amounts of potassium t-butoxide in t-butyl alcohol for several days . 

Hofmann degradation of the nonnatural protoberberine 454 afforded the 10-membered ring base 455 (65%) in addition to the styrene-type compound (13%) (Scheme 92). Dihydroxylation of the former with N-bromosuccinimide in the presence of a large excess of hydrochloric acid and subsequent oxidation of the product diol 456 with periodic acid afforded the dialdehyde 457. On irradiation in tert-butyl alcohol 457 provided ( )-cis-alpinigenine (445) along with ( )-alpinigenine (441) as a result of endo and exo intramolecular cycloaddition, respectively, of the intermediate photodienol (221,222). 

A concerted four-center cis addition leads to (52) and a trans adduct a trans addition, possibly via protonium species, leads to (53) and a cis adduct a stepwise cationic addition leads to (54) and a mixture of cis and trans adducts. Recent studies by Marshall and Wurth strongly indicate that intermediate (54) is correct. Irradiation of octalin (55) in aqueous /-butyl alcohol (DaO)-xylene results in formation of the equatorially deuterated alcohols (56) and (57) and the equatorially deuterated exocyclic olefin (58) ... 

Methyl isovalerate, azeotropic mixtures with butyl alcohols, 4 395t Methyl ketones, acetic anhydride used in synthesis, 1 148 Methyllithium, 14 249 15 147 Methylmagnesium chloride, 16 319 (R)-(—)-Methylmandelic acid chloride, chiral derivatizing reagent, 6 76t Methyl mercaptan production, 15 17 3-Methylmercaptopropionaldehyde (MMP), intermediate in methionine synthesis, 1 268, 269, 276... 

Alcohols, their corresponding olefins and alkyl cations are in equilibrium, with the alcohol generally predominating over the olefin (Purlee et al., 1955 Taft and Riesz, 1955 Boyd et al., 1960). The alkyl cation concentration is extremely low and this species never exists as more than a transient intermediate whose relation to the solvent is little known. In 5% H2SO4 the ratio of alcohol to olefin is about 1200 to 1 at 50° for the isobutylene-tertiary butyl alcohol system (Taft and Riesz, 1955). As the temperature increases the ratio of alcohol to olefin at equilibrium decreases (Boyd et al., 1960). This can be illustrated by examining the position of equilibrium in equation (8). Values of Kp, [alcohol (1)]/ [olefin (g)], were shown to vary from 5 54 at 50° to 1-34 at 70°. The equilibrium constant [alcohol (l)]/[olefin (1)] can be calculated from... 

In this range of acidity the intermediate carbonium ions do not fragment to smaller species. Isobutylene (C4) produces Cg and C12 olefins but no C5, C(), C7, C9 Cio or Cu products. This lack of fragmentation has been demonstrated for the co-polymerization of secondary and tertiary butyl alcohols and for mixed butyl and amyl alcohols (Whitmore and Mixon, 1941 Whitmore et al., 1941). 

Alkyl cations are thus not directly observed in sulphuric acid systems, because they are transient intermediates present in low concentrations and react with the olefins present in equilibrium. From observations of solvolysis rates for allylic halides (Vernon, 1954), the direct observation of allylic cation equilibria, and the equilibrium constant for the t-butyl alcohol/2-methylpropene system (Taft and Riesz, 1955), the ratio of t-butyl cation to 2-methylpropene in 96% H2SO4 has been calculated to be 10 . Thus, it is evident that sulphuric acid is not a suitable system for the observation of stable alkyl cations. In other acid systems, such as BFj-CHsCOOH in ethylene dichloride, olefins, such as butene, alkylate and undergo hydride transfer producing hydrocarbons and alkylated alkenyl cations as the end products (Roberts, 1965). This behaviour is expected to be quite general in conventional strong acids. 

Uses. Intermediate for the production of scorbic acid formerly used in the manufacture of -butyl alcohol formed during the combustion of fossil fuels... 

Tertiary alcohols dehydrate most readily, primary alcohols least readily, and, unsurprisingly, secondary alcohols are intermediate. This relates to the relative stability of the intermediate carbocation. The temperature and concentration of the acid depends upon the type of alcohol. A primary alcohol, such as ethanol, requires concentrated acid and a very high temperature (180 degrees Celsius), while a tertiary alcohol, such as t-butyl alcohol, requires 20 percent sulfuric acid at 85 to 90 degrees Celsius. The process follows an El mechanism and produces the thermodyncimically more stable product. 

Intermediate products which have been identified by isolation or inferred as precursors of butyric acid, butyl alcohol, acetone and isopropyl alcohol are acetaldehyde, acetaldol, pyruvic acid and its aldol,... 

SCHEME 23. Processes taking place during ozonolysis of t-butyl alcohol in aqueous media, involving intermediate formation of a tetroxy compound... 

Because salicylic acid contains the deactivating meta-directing carboxyl group, Friedel-Crafts reactions are generally inhibited. This effect is somewhat offset by the presence of the activating hydroxyl group. Salicylic acid reacts with isobutyl or /-butyl alcohol in 80 wt % sulfuric acid at 75°C to yield 5-/-butylsalicylic acid [16094-31-8], In the case of isobutyl alcohol, the intermediate carbonium ion rearranges to (CH3)3C+. 

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