Dimethylpentane reaction

When optically pure 2 3 dimethyl 2 pentanol was subjected to dehydration a mixture of two alkenes was obtained Hydrogenation of this alkene mixture gave 2 3 dimethylpentane which was 50% optically pure What were the two alkenes formed in the elimination reaction and what were the relative amounts of each" ... 

Propylene. Propylene alkylation produces a product that is rich in dimethylpentane and has a research octane typically in the range of 89—92. The HF catalyst tends to produce somewhat higher octane than does the H2SO4 catalyst because of the hydrogen-transfer reaction, which consumes additional isobutane and results in the production of trimethylpentane and propane. 

The reactions proceed via carbenium ions in a chain mechanism, initiated by the reaction between an olefin and an acid to C-C -C, which then reacts with iso-butane to give C-C C)-C. This carbenium ion is the central species in propagation steps to alkylated products such as 2,2-dimethylpentane and related products (Fig. 9.14). 

The peroxyl radical of a hydrocarbon can attack the C—H bond of another hydrocarbon. In addition to this bimolecular abstraction, the reaction of intramolecular hydrogen atom abstraction is known when peroxyl radical attacks its own C—H bond to form as final product dihydroperoxide. This effect of intramolecular chain propagation was first observed by Rust in the 2,4-dimethylpentane oxidation experiments [130] ... 

During PP oxidation, hydroxyl groups are formed by the intramolecular isomerization of alkyl radicals. Since PP oxidizes through an intense intramolecular chain transfer, many of the alkyl radicals containing hydroperoxy groups in the 0-position to an available bond can undergo this reaction. An isomerization reaction has also been demonstrated for the liquid-phase oxidation of 2,4-dimethylpentane [89], Oxidation products contain, in addition to hydroperoxides, oxide or diol. 

The highly branched 1,1-dimethylcyclopentane (1,1-DMCP) not only has the highest ON among the four RC isomers, but also some of its RO products have exceptional ON (e.g. the RON of 1,1-dimethylpentane is 92). This product can be obtained by using metal catalysts which selectively open at secondary-secondary C-C bonds. As discussed earlier, Ir/Si02 is best suited for this reaction. 

Photolytic. A photooxidation rate constant of 3.4 x lO" cmVmolecule-sec was reported for the gas-phase reaction of 2,3-dimethylpentane and OH radicals (Atkinson, 1990). 

Use the structure-reactivity relationship approach to calculate the rate constants for the reactions of OH with the following compounds and calculate the percentage difference from the recommended values in Table 6.2 (a) ethane, (b) n-butane, (c) 2-methylpen-tane, (d) 2,2-dimethylpentane, (e) 2,2,3-trimethyl-butane, (f) n-nonane, (g) n-decane. 

The complex nature of alkylation of alkenes is illustrated by the reaction of 1- and 2-chloropropane with ethylene,53 which does not yield the expected isopentyl chloride. Instead, l-chloro-3,3-dimethylpentane is formed by isomerization of the primary product to give fcrf-amyl chloride, which adds to ethylene more readily than do starting propyl halides (Scheme 5.4). The same product is also obtained54 when ethylene reacts with neopentyl chloride in the presence of AICI3. 

Dimethylpentane-2,4-diol chromate(VI) diester (1). The diol is prepared by reaction of diacetone alcohol with 2 equiv. of CH3Li (ether, -70-0°), 97% crude yield. The chromate ester (1) is obtained by reaction of the diol in CC14 with Cr03 after about 10 minutes P205 is added and then the clear solution is stored for use. 

Using chromium-based oxidants 2,4-Dimethylpentane-2,4-diol chromate(VI) diester, 122 Trimethylsilyl chlorochromate, 327 Using other oxidizing agents Bis(tributyltin) oxide, 41 Hydrogen hexachloroplatinate(IV)-Copper(II) chloride, 145 4-Methoxy-2,2,6,6-tetramethyl-1 -oxopiperidinium chloride, 183 Osmium tetroxide, 222 Potassium nitrosodisulfonate, 258 Samarium(II) iodide, 270 From alkenes by addition or cleavage reactions... 

The 2,3-dimethyl-1-pentene formed in the dehydration reaction must be optically pure because it arises from optically pure alcohol by a reaction that does not involve any of the bonds to the stereo-genic center. When optically pure 2,3-dimethyl-l-pentene is hydrogenated, it must yield optically pure 2,3-dimethylpentane—again, no bonds to the stereogenic center are involved in this step. 

The 2,3-dimethyl-2-pentene formed in the dehydration reaction is achiral and must yield racemic 2,3-dimethylpentane on hydrogenation. 

In a similar respect, ionization of 2,4-dichloro-2,4-dimethylpentane (6) does not give the 1,3-carbodication (7, eq 3).3 Despite the superacidic conditions, deprotonation occurs to give the allylic cation (8). Even substitution by phenyl groups is not enough to stabilize the 1,3-dication. For example 1,1,3,3-tetraphenyl-l,3-propanediol (9) also undergoes the deprotonaton or disproportionation reactions (eq 4).3... 

No benzodiazepine has been obtained from o-phenylenediamine and 3,3-dimethylpentane-2,4-dione (38MI1 40MI1, 40MI2 63JA3354 75TL91) a monoacylated 2,3-diaminophenazine formed by self-condensation of two molecules of the diamine and subsequent reaction with the diketone has been isolated from the reaction mixture. It is possible that diazepine formation requires the presence of some enol form of a diketone. 

As can be deduced from discussions presented above and in Chapter 5, it is very important to recognize that when designing reactions involving carbocations, both migration reactions and elimination reactions can complicate the outcome of intended SnI transformations. An example illustrating the potential formation of multiple side products is shown in Scheme 6.3 with the solvolysis of 2-bromo-2,3-dimethylpentane in methanol. 

Criegee and Paulig83 obtained the substituted 1,2-dioxolan (78) in 31% yield by reaction of 2,4-dimethylpentane-2,4-diol with 80% hydrogen peroxide (route B). 

The reaction of isopentane with ethylene under the same conditions as those used for n -pentane resulted in about the same yield of heptanes (31%) and a very small amount of higher-boiling product (Expt. 11). The heptanes consisted of more than 6.5 times as much 3,3-dimethylpentane as 2,3-dimethylpentane. It may be concluded that abstraction of the single hydrogen attertiary carbon atom takes place much more readily than does abstraction of one of the two hydrogen atoms attached to the secondary (penultimate) carbon atoms. 

The product formed in largest amount by the hydrochloric acid-promoted and peroxide-induced reaction of isopentyl chloride with ethylene was also that formed by alkylation at the tertiary carbon atom, namely 1-chloro-3,3-dimethylpentane (Ig.) (Expt. 25). The remaining constituents of the reaction product were all obtained in very minor amount and were all alkyl chlorides. Among these were 4-chloro-2-methylhexane (y), 1-chlorohexane (formed by telomerization) and some chlorononanes including 5-chloro-3,3-dimethyl-heptane (3 ) formed by ethylation of 12, 4-chloro-2-methyloctane (15) and l-chloro-3-methyloctane (IT). ... 

The synergistic effect often observed in bimetallic systems was further explored by Garland and coworkers. The hydroformylation of 3,3-dimethylbut-l-ene to form 4,4-dimethylpentanal in >95% selectivity at room temperature with [Rli4(CO)i2]-[Mn2(CO)io/HMn(CO)5] as catalyst coprecursors was investigated using in situ PT-IR spectroscopic techniques and kinetic studies revealing evidence of a bimetallic catalytic binuclear elimination reaction (CBER). 

Cycloheptenones. Dehalogenation of z,x -dibromoketoncs with diiron nonacarbonyl in the presence of a 1,3-diene provides a direct route to seven-membered cyclic ketones. Thus the reaction of 2,4-dibromo-2,4-dimethylpentane-3-one (I), diiron... 

It has been stated that a formyl group formed during the hydrofoimylation reaction of unfunctionalized olefins is unlikely to be attached to a quaternary carbon atom (the Keulemans rule). An example of this general rule is the oxo reaction with 2,3-dimethyl-2-butene, where 3,4-dimethylpentanal is formed exclusively. For both rhodium and cobalt catalysts, isomerization of the substrate is followed by hydrofoimylation (Scheme 1) [47, 48]. 

Isotopic exchange is unaccompanied by skeletal isomerization. In particular, even when Do is reduced to 10%, 3,3-dimethylpentane is unisomerized (11). This makes it unlikely that carbonium ion reactions are involved. 

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