2- Pentanone bromination

Fig. 1 Acidity function-rate profile for 3-pentanone bromination in sulphuric acid (data taken from Ballabio et al., 1974)...

Pentanone 3- Pentanone Perchlorates Bromine trifluoride Hydrogen peroxide, nitric acid Carbonaceous materials, finely divided metals particularly magnesium and aluminum, sulfur, benzene, olefins, ethanol, sulfur, sulfuric acid... 

Reduction of 2-bromo-3-pentanone at mercury affords a mixture of 3-pentanone and l-hydroxy-3-pentanone, whereas electrolysis of Q ,Q -dibromoacetone in the presence of benzoate gives a mixture of products arising from both a carbon-bromine bond cleavage and an Sn2 displacement of bromide by benzoate [94]. In an acetic acid-acetate buffer, branched dibromo ketones, such as 2,4-dibromo-2,4-dimethyl-3-pentanone, are reduced to a-acetoxy ketones however, less highly substituted compounds, such as 4,6-dibromo-5-nonanone, undergo simple cleavage of both carbon-bromine bonds [95]. Other work dealing with the reduction of Q, Q -dibromoketones has been described [96]. 

A. 2,4-Dibromo-3-pentanone (1). A three-necked, 250-ml. flask is fitted with a stirrer, a dropping funnel, and a condenser protected by a calcium chloride drying tube. Bromine (160 g., 1 mole) is added rapidly to a stirred solution of 45 g. (0.52 mole) of 3-pentanone (Note 1) and 1 ml. of phosphorus tribromide maintained between —10° and 0° with a dry ice-acetone bath in an efficient hood. Toward the end of the reaction very large amounts of hydrogen bromide are evolved, and the rate of addition must be controlled to allow the hood to exhaust the gas. Alternatively, a... 

Oxidizer, Poison, Corrosive SAFETY PROFILE Poisonous and corrosive. Very reactive, a powerful oxidizer. Explosive or violent reaction with organic materials, water, acetone, ammonium halides, antimony, antimony trichloride oxide, arsenic, benzene, boron, bromine, carbon, carbon monoxide, carbon tetrachloride, carbon tetraiodide, chloromethane, cobalt, ether, halogens, iodine, powdered molybdenum, niobium, 2-pentanone, phosphoms, potassium hexachloroplatinate, pyridine, silicon, silicone grease, sulfur, tantalum, tin dichloride, titanium, toluene, vanadium, uranium, uranium hexafluoride. 

Acid-catalyzed bromination of 2-pentanone (CHgCOCHgCHgCHg) forms two products BrCHgCOCHgCHgCHs (A) and CH3COCH(Br)CH2CHg (B). Explain why the major product is B, with the Br atom on the more substituted side of the carbonyl group. 

Like chlorine, bromine is used to convert secondary alcohols into ketones. A convenient way is to apply the addition product of 2 mol of bromine with l,4-diazabicyclo[2,2,2]octane (Dabco), a nonhygroscopicyellow solid, prepared by mixing carbon tetrachloride solutions of bromine and Dabco. The compound decomposes at 155-160 °C [726]. Oxidation with this addition product is carried out in acetonitrile solution at 50 °C and results in 50 and 71% yields of cyclopentanone and cyclohexanone, respectively, but very low yields of 2-pentanone [726]. 

PENTANONE-2 or 2-PENTANONE (107-87-9) Forms explosive mixture with air (flash point 45°F/7°C). Reacts violently with strong oxidizers, aldehydes, bromine trifluoride, hydrogen peroxide, nitric acid, perchloric acid. Attacks some plastics, rubber, and coatings. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

Propose a mechanism for the reaction of 3-pentanone with sodium hydroxide and bromine to give 2-bromo-3-pentanone. 

For example, bromination of 3-pentanone gives mostly 2,2-dibromo-3-pentanone. After one hydrogen is replaced by bromine, the enolate ion is stabilized by both the carbonyl group and the bromine atom. A second bromination takes place faster than the first Notice that the second substitution takes place at the same carbon atom as the first,... 

Propose a mechanism for the acid-catalyzed bromination of 3-pentanone. 

Predict the position of acid-catalyzed bromination of each of the following ketones (a) 2-butanone, (b) 2-pentanone, (c) 3-methyl-2-butanone, (d) 2-methylcyclohexanone, and (e) methyl cyclohexyl ketone. 

Thioformamide is utilized for the synthesis of 2-unsubstituted 5-trifluoromethylthiazoles. Thus, 5-methoxy-l,l,l-trifluoro-2-pentanone gave 5-(methoxyethyl)-4-trifluoromethylthiazole in reasonable total yield on bromination with BBrs followed by treatment with thioformamide [89]. 

Write the product of the reaction of bromine with 2,2-dimethyl-3-pentanone under acidic and basic conditions. 

Under acidic conditions, one bromine atom replaces a hydrogen atom at C-4 to give 2-bromo-4,4-dimethyl-3-pentanone. Under basic conditions, the reaction continues to replace the second hydrogen atom faster than the first, and a dibromo compound is obtained. 

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