Ethylenic acetals, bromination

Therefore the di-brom ethane which yields acet-aldehyde must be the one in which the two bromine atoms are linked to the same carbon atom, i.e., the unsymmetncal compound. The other compound then must have the two bromine atoms each linked to a different carbon atom, i.e., it must be the symmetrical compound. Now it is this last compound, not the first, which is obtained when ethylene reacts with bromine and adds on two bromine atoms. For this reason it is known as ethylene bromide. Our reaction between ethylene and bromine must be represented, then, as follows ... 

Bromoethyl esters The cleavage of ethylene acetals using bromoform as bromine source is achieved by refluxing in benzene, also in the presence of AIBN and TsOH. 

Dehydration of the optically active relay (178) derived from enmein (62) gave a 1 2 mixture of 5,6-ene and 6,7-ene. Separation could be achieved by means of the ethylene acetal (187), whose ozonolysis product was subjected to successive Jones oxidation, methylation, Wittig reaction, and treatment with dilute hydrochloric acid to afford the 3-on-16-ol derivative (188). Bromination of (188) followed by dehydrobromination and subsequent dehydration afforded (189). The purified compound (189), after conversion into the acetal, was hydrolyzed to carboxylic acid (190), which was transformed into the desired lactone (191) by treatment with boron trifluoride etherate. The reaction produced a single product uncontaminated by the C-1 epimer, because of easy formation of a favored transition state which satisfied the stereoelectronic requirements. 

Cyclodecanone ethylene acetal is converted by bromination-dehydro-bromination and hydrolysis into cyclodec-2-enone, apparently as the transisomer the latter is condensed with hydrazines to give pyrazolophanes. Various condensations of cyclododecanone are also reported. ... 

Bromoacetic acid can be prepared by the bromination of acetic acid in the presence of acetic anhydride and a trace of pyridine (55), by the HeU-VoUiard-Zelinsky bromination cataly2ed by phosphoms, and by direct bromination of acetic acid at high temperatures or with hydrogen chloride as catalyst. Other methods of preparation include treatment of chloroacetic acid with hydrobromic acid at elevated temperatures (56), oxidation of ethylene bromide with Aiming nitric acid, hydrolysis of dibromovinyl ether, and air oxidation of bromoacetylene in ethanol. 

The procedure described is essentially that of Belleau and Weinberg and represents the only known way of obtaining the title compound. One other quinone acetal, 1,4,9,12-t6traoxadispiro[4.2.4.2]tetradeea-6,13-diene, has been synthesized by a conventional method (reaction of 1,4-cyclohexanedione with ethylene glycol followed by bromination and dehydrobromination ) as well as by an electrochemical method (anodic oxidation of 2,2-(l,4-phenylenedioxy)diethanol ). Quinone acetals have been used as intermediates in the synthesis of 4,4-dimethoxy-2,5-cyclohexadienone,. syw-bishomoquinone, - and compounds related to natural products. ... 

Table 5 shows the rate ratios between ethylenes differing by an increase by two in number of alkyl substituents. It can be observed that in solvents as different as methanol, ethanol, and acetic acid, the rate ratio is always around 10, that is of the same order of magnitude of the increase in Kf. This indicates that substituent effects are not much more influential on the kinetic constants that on Kf. A possible rationalization of the lower accelerating effects by alkyl substituents on the bromination rate, relative to what could be expected for an AdgCl mechanism on... 

Bromoacetic acid has been prepared by direct bromination of acetic acid at elevated temperatures and pressures,2-3-4 or with dry hydrogen chloride as a catalyst 6 and with red phosphorus as a catalyst with the formation of bromoacetyl bromide.6-7-8-9-19 Bromoacetic acid has also been prepared from chloroacetic acid and hydrogen bromide at elevated temperatures 6 by oxidation of ethylene bromide with fuming nitric acid 7 by oxidation of an alcoholic solution of bromoacetylene by air 8 and from ethyl a,/3-dibromovinyl ether by hydrolysis.9 Acetic acid has been converted into bromoacetyl bromide by action of bromine in the presence of red phosphorus, and ethyl bromoacetate has been... 

If the ethylene produced with sulphuric acid is analysed (method ) it is found that very much carbon monoxide is present. The phosphoric acid method is better suited for the production of the pure gas, but the best way is to remove with zinc dust and glacial acetic acid the bromine from the ethylene dibromide already prepared. The dibromide is dropped into a suspension of an excess (not too great) of zinc dust in alcohol and glacial acetic acid (2-5 moles) and the ethylene is collected over water in a gas-holder. 

Marchand and co-workers ° synthesis of 5,5,9,9-tetranitropentacyclo[5.3.0.0 .0 °.0 ] decane (52) reqnired the dioxime of pentacyclo[5.3.0.0 .0 °.0 ]decane-5,9-dione (49) for the incorporation of the four nitro groups. Synthesis of the diketone precursor (48) was achieved in only five steps from cyclopentanone. Thus, acetal protection of cyclopentanone with ethylene glycol, followed by a-bromination, and dehydrobromination with sodium in methanol, yielded the reactive intermediate (45), which underwent a spontaneous Diels-Alder cycloaddition to give (46). Selective acetal deprotection of (46) was followed by a photo-initiated intramolecular cyclization and final acetal deprotection with aqueous mineral acid to give the diketone (48). Derivatization of the diketone (48) to the corresponding dioxime (49) was followed by conversion of the oxime groups to gem-dinitro functionality using standard literature procedures. 

The superfluous bromine is then removed by reduction with zinc in acetic acid (26-1). The 20 ketone is next protected against the strongly reducing conditions in the subsequent step by conversion to the ethylene glycol acetal (26-2). Birch reduction with lithium in liquid ammonia in the presence of ethanol proceeds as usual to the dihydrobenzene (26-3). Treatment of this last product with mineral acid serves to hydrolyze both the enol ether at the 3 position and the acetal at the... 

According to both the NFPA Guide and Bretherick (Refs 5 13), sulfuric acid causes explosions and/or fires when in intimate contact with a large number (over 70) of materials including acetic anhydride, acet and nitric acid, acrolein, alcohols, alcohols and hydrogen peroxide, anun hydroxide, aniline, bromine and metals, carbides, chlorates, cyclopentadiene, ethylene glycol, various hydrocarbons, hydrochloric acid, iron, mercuric nitride, powdered metals, perchlorates, picrates, pyridine, Na carbonate, steel, sucrose, vinyl acetate, and w. Illustrative... 

A powerful oxidizer. Explosive reaction with acetaldehyde, acetic acid + heat, acetic anhydride + heat, benzaldehyde, benzene, benzylthylaniUne, butyraldehyde, 1,3-dimethylhexahydropyrimidone, diethyl ether, ethylacetate, isopropylacetate, methyl dioxane, pelargonic acid, pentyl acetate, phosphoms + heat, propionaldehyde, and other organic materials or solvents. Forms a friction- and heat-sensitive explosive mixture with potassium hexacyanoferrate. Ignites on contact with alcohols, acetic anhydride + tetrahydronaphthalene, acetone, butanol, chromium(II) sulfide, cyclohexanol, dimethyl formamide, ethanol, ethylene glycol, methanol, 2-propanol, pyridine. Violent reaction with acetic anhydride + 3-methylphenol (above 75°C), acetylene, bromine pentafluoride, glycerol, hexamethylphosphoramide, peroxyformic acid, selenium, sodium amide. Incandescent reaction with alkali metals (e.g., sodium, potassium), ammonia, arsenic, butyric acid (above 100°C), chlorine trifluoride, hydrogen sulfide + heat, sodium + heat, and sulfur. Incompatible with N,N-dimethylformamide. 

The procedure for the elimination of HBr from the dibromo ester is a modification of the method of Lawton and co-workers for sui generis generation of the methyl or ethyl ester during a reaction. Methyl a-(bromomethyl)acrylate has also been prepared by bromination of methyl methacrylate in 700°C steam and by dehydrohalogenation with sodium acetate in acetic acid. Ethyl a-(bromomethyl)acrylate has been prepared by dehydrohalogenation with the monosodium salt of ethylene glycoP and ethyl diisopropylamine." The latter reaction was reported by Ohler et al. with no experimental details for the elimination reaction. The use of triethylamine as reported in this procedure appears to be the most efficient and convenient method for dehydrobromination to these acrylate esters. 

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