Ketone decomposition

Dinitrophenylhydra2ones usually separate in well-formed crystals. These can be filtered at the pump, washed with a diluted sample of the acid in the reagent used, then with water, and then (when the solubility allows) with a small quantity of ethanol the dried specimen is then usually pure. It should, however, be recrystallised from a suitable solvent, a process which can usually be carried out with the dinitrophenylhydrazones of the simpler aldehydes and ketones. Many other hydrazones have a very low solubility in most solvents, and a recrystallisation which involves prolonged boiling with a large volume of solvent may be accompanied by partial decomposition, and with the ultimate deposition of a sample less pure than the above washed, dried and unrecrystal-lised sample. 

Note. The 2,4-dinitrophenylhydrazones of many higher aldehydes and ketones may be insoluble in most solvents. In this case, Mter them off, wash with ethanol, dry and take the m.p. attempted recrystallisation may cause partial decomposition. (M.ps., pp. 530-540.)... 

The complete assembly for carrying out the catalytic decomposition of acids into ketones is shown in Fig. Ill, 72, 1. The main part of the apparatus consists of a device for dropping the acid at constant rate into a combustion tube containing the catalyst (manganous oxide deposited upon pumice) and heated electrically to about 350° the reaction products are condensed by a double surface condenser and coUected in a flask (which may be cooled in ice, if necessary) a glass bubbler at the end of the apparatus indicates the rate of decomposition (evolution of carbon dioxide). The furnace may be a commercial cylindrical furnace, about 70 cm. in length, but it is excellent practice, and certainly very much cheaper, to construct it from simple materials. 

Aromatic ketones usually have relatively high boiling points, but distil with little or no decomposition. Many are solids. The vapours generally burn with a smoky flame. They react with the 2 4-dinitrophenyll hydrazine reagent (Section 111,74,/) or with the phenylhydrazine reagent... 

The rt,/3-unsaturated linear carbonyl compound 39 is obtained by the decomposition of the cyclic hydroperoxide 38 with PdCl2,[35]. The a, 0-epoxy ketone 40 is isomerized to the /3-diketone 41 with Pd(0) catalyst[36]. The 1,4-epiperoxide 42 is converted into the /3-hydroxy ketone 43 and other products[37]. 

The physical and chemical properties are less well known for transition metals than for the alkaU metal fluoroborates (Table 4). Most transition-metal fluoroborates are strongly hydrated coordination compounds and are difficult to dry without decomposition. Decomposition frequently occurs during the concentration of solutions for crysta11i2ation. The stabiUty of the metal fluorides accentuates this problem. Loss of HF because of hydrolysis makes the reaction proceed even more rapidly. Even with low temperature vacuum drying to partially solve the decomposition, the dry salt readily absorbs water. The crystalline soflds are generally soluble in water, alcohols, and ketones but only poorly soluble in hydrocarbons and halocarbons. 

The limitations of this reagent are several. It caimot be used to replace a single unactivated halogen atom with the exception of the chloromethyl ether (eq. 5) to form difluoromethyl fluoromethyl ether [461 -63-2]. It also caimot be used to replace a halogen attached to a carbon—carbon double bond. Fluorination of functional group compounds, eg, esters, sulfides, ketones, acids, and aldehydes, produces decomposition products caused by scission of the carbon chains. 

Okfm Syntheses. Conversion of aldehydes and ketones to olefins by the base-catalyzed decomposition of -toluenesulfonic (Ts) acid hydrazones (10) is known as the Bamford-Stevens reaction (54,55). 

An alternative chain-terminating decomposition of the tetroxide, known as the Russell mechanism (29), can occur when there is at least one hydrogen atom in an alpha position the products are a ketone, an alcohol and oxygen (eq. 15). This mechanism is troubling on theoretical grounds (1). Questions about its vaUdity remain (30), but it has received some recent support (31). 

The radicals are then involved in oxidations such as formation of ketones (qv) from alcohols. Similar reactions are finding value in treatment of waste streams to reduce total oxidizable carbon and thus its chemical oxygen demand. These reactions normally are conducted in aqueous acid medium at pH 1—4 to minimize the catalytic decomposition of the hydrogen peroxide. More information on metal and metal oxide-catalyzed oxidation reactions (Milas oxidations) is available (4-7) (see also Photochemical technology, photocatalysis). 

Decomposition late studies on dialkyl peioxydicaibonates ia vaiious solvents leveal diamatic solvent effects that ptimatily lesult fiom the susceptibiUty of peioxydicaibonates to iaduced decompositions. These studies show a decieasiag oidei of stabiUty of peioxydicaibonates ia solvents as follows TCE > saturated hydrocarbons > aromatic hydrocarbons > ketones (29). Decomposition rates are lowest in TCE where radicals are scavenged before they can induce the decomposition of peroxydicarbonate molecules. 

Eithei oxidation state of a transition metal (Fe, Mn, V, Cu, Co, etc) can activate decomposition of the hydiopeioxide. Thus a small amount of tiansition-metal ion can decompose a laige amount of hydiopeioxide. Trace transition-metal contamination of hydroperoxides is known to cause violent decompositions. Because of this fact, transition-metal promoters should never be premixed with the hydroperoxide. Trace contamination of hydroperoxides (and ketone peroxides) with transition metals or their salts must be avoided. 

Thermal Stability. The saturated C —C 2 ketones are thermally stable up to pyrolysis temperatures (500—700°C). At these high temperatures, decomposition can be controlled to produce useful ketene derivatives. Ketene itself is produced commercially by pyrolysis of acetone at temperatures just below 550°C (see Ketenes, ketene dil rs, and related substances). 

Some unsaturated ketones derived from acetone can undergo base- or acid-catalyzed exothermic thermal decomposition at temperatures under 200°C. Experiments conducted under adiabatic conditions (2) indicate that mesityl oxide decomposes at 96°C in the presence of 5 wt % of aqueous sodium hydroxide (20%), and that phorone undergoes decomposition at 180°C in the presence of 1000 ppm iron. The decomposition products from these reactions are endothermic hydrolysis and cleavage back to acetone, and exothermic aldol reactions to heavy residues. 

Commercial lecithin is insoluble but infinitely dispersible in water. Treatment with water dissolves small amounts of its decomposition products and adsorbed or coacervated substances, eg, carbohydrates and salts, especially in the presence of ethanol. However, a small percentage of water dissolves or disperses in melted lecithin to form an imbibition. Lecithin forms imbibitions or absorbates with other solvents, eg, alcohols, glycols, esters, ketones, ethers, solutions of almost any organic and inorganic substance, and acetone. It is remarkable that the classic precipitant for phosphoHpids, eg, acetone, dissolves in melted lecithin readily to form a thin, uniform imbibition. Imbibition often is used to bring a reactant in intimate contact with lecithin in the preparation of lecithin derivatives. 

Yields of excited states from 1,2-dioxetane decomposition have been determined by two methods. Using a photochemical method (17,18) excited acetone from TMD is trapped with /n j -l,2-dicyanoethylene (DCE). Triplet acetone gives i7j -l,2-dicyanoethylene with DCE, whereas singlet acetone gives 2,2-dimethyl-3,4-dicyanooxetane. By measuring the yields of these two products the yields of the two acetone excited states could be determined. The yields of triplet ketone (6) from dioxetanes are determined with a similar technique. 

Dioxetanones decompose near or below room temperature to aldehydes or ketones (56). The decomposition reactions are weakly chemiluminescent Qc ca 10 ein/mol) because the products are poorly fluorescent. However, addition of 10 M mbrene provides 2iQc ca 10 ein/mol, and 2iQc on the order of was calculated at mbrene concentrations above 10 M after correcting for yield loss factors (57). The decomposition rates are first order ia... 

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

Decomposition products from primary and secondary dialkyl peroxides include aldehydes, ketones, alcohols, hydrogen, hydrocarbons, carbon monoxide, and carbon dioxide (44). 

Because di-/ fZ-alkyl peroxides are less susceptible to radical-induced decompositions, they are safer and more efficient radical generators than primary or secondary dialkyl peroxides. They are the preferred dialkyl peroxides for generating free radicals for commercial appHcations. Without reactive substrates present, di-/ fZ-alkyl peroxides decompose to generate alcohols, ketones, hydrocarbons, and minor amounts of ethers, epoxides, and carbon monoxide. Photolysis of di-/ fZ-butyl peroxide generates / fZ-butoxy radicals at low temperatures (75), whereas thermolysis at high temperatures generates methyl radicals by P-scission (44). 

Thermal decompositions of di-Z fZ-cycloalkyl peroxides produce Z fZ-cycloalkoxy radicals which undergo ring -scission to give acycHc ketones,diketones, and other products (44) ... 

Thermal decomposition of dihydroperoxides results in initial homolysis of an oxygen—oxygen bond foUowed by carbon—oxygen and carbon—carbon bond cleavages to yield mixtures of carbonyl compounds (ketones, aldehydes), esters, carboxyHc acids, hydrocarbons, and hydrogen peroxide. 

Thermal and photochemical decomposition of peroxides (4) and (5) lacking a-hydrogens (those derived from ketones) produces macrocycHc hydrocarbons andlactones (119,152,153). For example, 7,8,15,16,23,24-hexaoxatrispiro [5.2.5.2.5.2] tetracosane (see Table 5) yields cyclopentadecane and oxacycloheptadecan-2-one. 

Substantial decomposition of phenoHc resins begins above 300°C. In the presence of oxygen, the methylene bridging group is converted to a hydroperoxide which in turn yields alcohols and ketones on decomposition. 

Alkaline earth metal alkoxides decompose to carbonates, olefins, hydrogen, and methane calcium alkoxides give ketones (65). For aluminum alkoxides, thermal stability decreases as follows primary > secondary > tertiary the respective decomposition temperatures are ca 320°C, 250°C, and 140°C. Decomposition products are ethers, alcohols, and olefins. 

When sublimed, anthraquinone forms a pale yeUow, crystalline material, needle-like in shape. Unlike anthracene, it exhibits no fluorescence. It melts at 286°C and boils at 379°—381°C. At much higher temperatures, decomposition occurs. Anthraquinone has only a slight solubiUty in alcohol or benzene and is best recrystallized from glacial acetic acid or high boiling solvents such as nitrobenzene or dichlorobenzene. It is very soluble in concentrated sulfuric acid. In methanol, uv absorptions of anthraquinone are at 250 nm (e = 4.98), 270 nm (4.5), and 325 nm (4.02) (4). In the it spectmm, the double aUyflc ketone absorbs at 5.95 p.m (1681 cm ), and the aromatic double bond absorbs at 6.25 p.m (1600 cm ) and 6.30 pm (1587 cm ). 

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

---