Hydrogenation 2-methyl-3-butyne

The primary source of isoprene today is as a by-product in the production of ethylene via naphtha cracking. A solvent extraction process is employed. Much less isoprene is produced in the crackers than butadiene, so the availability of isoprene is much more limited. Isoprene also may be produced by the catalytic dehydrogenation of amylenes, which are available in C-5 refinery streams. It also can be produced from propylene by a dimerization process, followed by isomerization and steam cracking. A third route involves the use of acetone and acetylene, produced from coal via calcium carbide. The resulting 3-methyl-butyne-3-ol is hydrogenated to methyl butanol and subsequently dehydrogenated to give isoprene. The plants that were built on these last two processes have been shut down, evidently because of the relatively low cost of the extraction route. 

The palladium-polyvinyl alcohol catalyst has proved useful in the reduction of acetylenes to ethylenes (15). Thus, 3-methyl-butyn-l-ol-3 has been reduced to 3-methyl-buten-l-ol-3 in excellent yield. Furthermore it was also advantageously utilized in the hydrogenation of cystine, in which case only 10 mg. of palladium were required (15a), and in the catalytic hydrogenation of apozymase (15b). 

Methylbutynol. 2-Methyl-3-butyn-2-ol [115-19-5] prepared by ethynylation of acetone, is the simplest of the tertiary ethynols, and serves as a prototype to illustrate their versatile reactions. There are three reactive sites, ie, hydroxyl group, triple bond, and acetylenic hydrogen. Although the triple bonds and acetylenic hydrogens behave similarly in methylbutynol and in propargyl alcohol, the reactivity of the hydroxyl groups is very different. 

The labile hydroxyl group is easily replaced by treatment with thionyl chloride, phosphorous chlorides, or even aqueous hydrogen haUdes. At low temperatures aqueous hydrochloric (186) or hydrobromic (187) acids give good yields of 3-halo-3-methyl-l-butynes. At higher temperatures these rearrange, first to l-halo-3-methyl-1,2-butadienes, then to the corresponding 1,3-butadienes (188,189). 

Steacie, E. W. R., and A. F. Trotman-Dickenson The Reactions of Methyl Radicals. IV. The Abstractions of Hydrogen Atoms from Cyclic Hydrocarbons, Butynes, Amines, Alcohols, Ethers and Ammonia. J. chem. Physics 19, 329 (1951)-... 

Addition of acetylene to acetone results in the formation of 2-methyl-3-butyn-2-ol, which is hydrogenated to 2-methyl-3-buten-2-ol in the presence of a palladium catalyst. This product is converted into its acetoacetate derivative with diketene [38] or with ethyl acetoacetate [39]. The acetoacetate undergoes rearrangement when heated (Carroll reaction) to give 6-methyl-5-hepten-2-one ... 

The production of isoprene from acetylene and acetone is also possible. The acetylene is reacted with acetone to produce 2-methyl-3-butyn-2-ol which, by hydrogenation produces 2-methyl-3-butene-2-ol. Dehydration then yields isoprene. 

Formylation of 5,7-dihydroxy -( -propyl)-coumarin (1) provided on 8-formy-lated product (26). Treatment of the compound 26 with 3-chloro-3-methyl-l-butyne to introduce regioselectively the chromene 27 because the phenolic hydroxyl group at the C position was less accessible for formylated substitution because of a presumed hydrogen-bonding interaction. To construct the enantiomerically pure rra i-2,3-dimethyl chroman-4-ol system, Deshpande et al." ° used organoborone... 

The stereoselective synthesis of unsaturated oxetanes has recently been achieved by Feigenbaum and coworkers.Previous studies have indicated that photochemical cis-trans isomerization of enals is rapid and results in the formation of equivalent amounts of stereoisomeric alkene adducts. " For example, irradiation of rran.r-crotonaldehyde and 2,6-dimethylfuran produced a 1 1 mixture of alkenic isomers (174) and (175) in 64% yield. Irradiation of 4-trimethylsilylbutyn-2-one and furan provided with S 1 stereoselectivity the bicyclic oxetane (176) in which the methyl group occupies the exo position, presumably because of the small steric requirement of the triple bond. Desilyation of the protected al-kyne produced an alkynic oxetane which was hydrogenated under Lindlar conditions to bicyclic vinyl-oxetane (177) attempts to use the unprotected butyn-2-one gave low isolated yields of oxetane because of extensive polymerization. The stereochemical outcome thus broadens previous alkynyloxetane syn-theses and makes possible the preparation of new oxetane structures that may be synthetically useful. 

Ethoxy-2-methyl-3-butyn-2-ol, 2844 Ethylene oxide, Contaminants, 0829 Ethyl oxalyl chloride, 1456 Hydrogen peroxide, Coal, 4477 Hydrogen peroxide, Copper(ll) chloride, 4477... 

Make a model of ethyne. Now replace the hydrogens with methyl groups to get 2-butyne. Compare to 2-butene which exhibits cis-trans isomerism. Why does 2-butene show geometric isomerism but not 2-butyne ... 

Hydrogenation was carried out in n-hexane solution. The phenyl group stabilizes the alkyne by 3.4 kcal mol"1 relative to methyl stabilization as seen in 2-butyne. The entry above is the arithmetic mean of two separate experiments consisting of 9 hydrogenation runs each. 

M. Crespo-Quesada, M. Grasemann, N. Semagina, A. Renken, L. Kiwi-Minsker, Kinetics of the solvent-free hydrogenation of 2-methyl-3-butyn-2-ol over a structured Pd-based catalyst, Catal. Today 147 (2009) 247. 

Methyl-3-buten-2-ol 294 A solution of 2-methyl-3-butyn-2-ol (336 g, 4 moles) in an equal volume of light petroleum is treated with quinoline (16.8 g) and Lindlar catalyst (30 g) the mixture is cooled to 10° and shaken in an atmosphere of hydrogen until 4moles of hydrogen are absorbed. After about 3-5 h the absorption slackens markedly and the catalyst is then filtered off and the product purified by distillation through a filled column. 94% (323 g) of 2-methyl-3-buten-2-ol is obtained, having m.p. 97-98° and n 1.4141. 

Many monoterpenes are desired fragrances in perfumery and flavors in food. They are produced on a larger scale from acetone (C3) and ethyne (acetylene C2) involving repetitive synthetic steps (Fig. 5). Initially, acetone is ethynylated by acetylene in the presence of a base (sodium hydroxide, amines with sodium carbonate) yielding 3-butyn-2-ol (C5) which is partially hydrogenated in the presence of deactivated catalysts (Lindlar catalysts) to 2-methyl-3-buten-2-ol. This can be converted to the key intermediate 6-methyl-5-hepten-2-one (Cg) via two pathways, either by transetherification with methylpropenylether and subsequent oxa-CoPE rearrangement, or by transesterification with methyl acetoacetate and subsequent Carroll decarboxylation. 

In order to synthesize the C5 acetate, dimethoxyacetone obtained by oxidation of acetone is ethynylated to 4,4-dimethoxy-3-methyl-l-butyn-3-ol in the presence of sodium hydroxide. Partial catalytic hydrogenation of the alkynol leads to 4,4-di-methoxy-3-methyl-l-buten-3-ol as the C5 alcohol which rearranges in acetie anhydride to the C5 aeetal ester. Deprotection of the aldehyde funetion necessary before the WiTTIG alkenylation is achieved thermally in the presence of copper(II)-salt as catalyst. 

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