Ketones, methyl with halogens

Haloform reaction (Section 22.6) The reaction of a methyl ketone with halogen and base to yield a haloform (CHX3) and a carboxylic acid. 

In the haloform reaction, methyl ketones (and the only methyl aldehyde, acetaldehyde) are cleaved with halogen and a base. The halogen can be bromine, chlorine, or iodine. What takes place is actually a combination of two reactions. The first is an example of 12-4, in which, under the basic conditions employed, the methyl group is trihalogenated. Then the resulting trihalo ketone is attacked by hydroxide ion ... 

Likewise, when methyl ketones react with iodine in the presence of a base, complete halogenation occurs. 

With most ketones, base-promoted halogenation continues until the a carbon atom is completely halogenated. Methyl ketones have three a protons on the methyl carbon, and they undergo halogenation three times to give trihalomethyl ketones. 

The overall haloform reaction is summarized next. A methyl ketone reacts with a halogen under strongly basic conditions to give a carboxylate ion and a haloform. 

Many other groups may be present in the alcohol or phenol during alkylation. Dimethyl sulfate and chlorohydrins give chloro ethers. Halo ethers are also prepared by the action of this reagent on halogenated phenols, e.g., w-bromoanisole (91%)- Phenolic aldehydes are converted in excellent yields to alkoxy aldehydes with dimethyl sulfate or alkyl p-toluenesulfonates. The conversion of a phenolic ketone to an alkoxy ketone is illustrated by the preparation of p-methoxypropiophenone (88%). Phenolic acids, esters, and cyanides, and nitrophenols respond favorably to this method for methylation. The sodium salt of mandelic acid, C H, CHOHCOOH, is methylated with dimethyl sulfate to furnish, after acidification, a-methoxyphenylacetic acid (42%). ... 

Haloform reaction (Section 23.7B) A halogenation reaction of a methyl ketone (RCOCH3) with excess halogen, which results in formation of RCOO and CHX3 (haloform),... 

Lieben iodoform reaction. Cleavage of methyl ketones with halogens (mostly iodine) and base to carboxylic acids and haloform. 

Aromatic methyl ketones can be halogenated at the a-position with Oxone and sodium halide, however, corr5>eting halogenation of the aromatic ring is significant. Q, a-Dichloroketones can be synthesized from alkynes by reaction with Oxone in HCl/DMF (eq 83). Oxone consistently gave better results than MCPBA for this transformation. 

Unlike its acid-catalyzed counterpart, a halogenation in base cannot normally be limited to monosubstitution, and this limits its synthetic applications. Methyl ketones, however, undergo a novel C—C cleavage on treatment with halogens in aqueous base. 

Several types of ketones have been reduced in water (Fig. 87). Among them, acetophenone is the substrate of reference. Other methyl aryl kenones with ortho-, meta-, or para-substituents such as methyl, methoxy, halogens, cyano, or nitro groups, related alkyl phenyl ketones, with the alkyl groups being aliphatic chains or cycles, as well as nitro-, cyano-, or halogen-methyl groups have been also reduced in the water medium. Heterocyclic ketones are efficiently reduced... 

If a methyl ketone is allowed to undergo multiple halogenations under basic conditions, a carboxylic acid will ultimately be produced via the haloform reaction (Eq. 11.10). This reaction involves three sequential halogenations, followed by an addition-elimination. It only works with a methyl ketone, because three halogens are required to create a good enough... 

Hagemann s-ester a compound prepared by treating a mixture of formaldehyde and ethylacetoacetate with base and then with acid and heat, half-chair conformation the least stable conformation of cyclohexane, haloform reaction the reaction of a halogen and HO — with a methyl ketone, halogenation reaction with halogen (Br, Cl, Ij). 

The chemical resistance of polyarylates (polyester carbonate) is largely similar to that of polycarbonate, but their ester content causes a more favorable behavior in hydrocarbons and boiling water. Figure 5.342. They are resistant to dilute mineral acids and acidic and neutral aqueous salt solutions. Bases, aqueous solutions of ammonia, amines, and alkaline salt solutions destroy polyarylates by hydrolytic degradation. Polyarylates are not attacked by aliphatic hydrocarbons and alcohols with the exception of methyl alcohol they are swelled and often dissolved by aromatics, ketones, esters, and halogenated hydrocarbons [723]. 

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