Description
Ketones are a class of functional groups that contain an internal carbonyl (C = O) group and are connected to two alkyl groups. In contrast, aldehydes are a class of functional groups that contain an external carbonyl group, attatched to alkyl substituent and a hydrogen. Examples of ketones are acetone, cyclohexanone, diacetone alcohol, diisobutyl ketone, isophorone, methyl amyl ketone, methyl ethyl ketone (MEK), methyl isoamyl ketone, methyl isobutyl ketone, and methyl propyl ketone.
The ketones consist of some of the most toxic elements of essential oils. Some of these include thujone and pulegone. The toxic chemicals in this group can cause epileptic seizures, convulsions, abortive effects, and mental confusion. However, not all ketones are toxic. The non-toxic ketones may aid in dissolving mucus, dissolving fats, and wound healing. Some common chemicals in this group are jasmone (Jasmine), fenchone (Fennel), carvone (Coriander, Peppermint, Tagetes), menthone (Peppermint, Spearmint, Rose Geranium), and pinocamphone (Hyssop, Juniper Berry).
Application
The majority of the ketones are straight and branched chain aliphatic hydrocarbons that contain the double bonded carbon-oxygen functional group. This carbonyl group gives the ketones high solvency for a wide variety of natural and synthetic resins. This high solvency feature makes the ketones valuable solvents in the coating industries and in other applications involving the dissolving of an organic substance. The ketones as a class are miscible with most other organic solvents. Many of the ketones possess a high diluent tolerance for the less expensive aliphatic and aromatic solvents. In many coating formulations the ketone solvents provide the lowest practical solution viscosity for a certain percent resin solids. The ketones generally have lower densities than other oxygenated solvents, which allows more volume per unit weight formulations. This desirable feature enables the formulation of higher-solids coatings that can better meet Volatile Organic Compound (VOC) regulations and have the lowest practical solution viscosities. The lower surface tension values of the ketones help reduce the high surface tensions of the highsolids coating formulations. Diisobutyl ketone is particularly effective in reducing the surface tensions of high-solids coating formulations.
The industrially available ketones offer a wide range of evaporation rates for the various coating applications. A solvent with excellent solvency and a fast, intermediate or slow evaporation rate for a particular coating application is available in the commercially produced ketones. Major producers of the ketones include Eastman Chemical Company, Exxon Chemical Company, Hoechst Celanese Company, Shell Chemical Company, and Union Carbide Corporation. BASF Corporation produces the cyclic ketone cyclohexanone. Acetone the lowest boiling-point ketone is produced by The Dow Chemical Company, Exxon Chemical Company, and Texaco Chemical Company.
The largest single use for ketones is as solvents in the wide spectrum of coatings and lacquers. The low density, low surface tension, low viscosity, and high resin solvency of the ketones make these solvents ideal for a wide range of resin and polymeric compositions. The ketones with their wide range of evaporation rates enable the coating and lacquer manufacturers to select a solvent blend that will allow the formation of a suitable coating or lacquer film. Many of the solvent blends will contain one or two ketones along with diluents like the cheaper aliphatic and aromatic hydrocarbons. Many of the ketones have high aliphatic and aromatic hydrocarbon dilution ratios that allow high percentages of the cheaper hydrocarbon diluents in the coating and lacquer formulations. Some of the ketones used as fast and slow evaporating solvents in cellulose ester lacquers include acetone, methyl isobutyl ketone (MIBK), ethyl n-amyl ketone, diisobutyl ketone, and cyclohexanone. Cyclohexanone with its high aromatic dilution ratio imparts good blush resistance, flow, and working qualities to lacquers. Methyl isobutyl ketone is often blended with methyl ethyl ketone (MEK) for high-solids lacquers. High-solids coatings of acrylic, polyesters, alkyd, and acrylic/urethane resins often use solvent blends of MIBK and MEK.
Definition
ketones: Organic compounds thatcontain the carbonyl group (>C=O)linked to two hydrocarbon groups.The ketone group is a carbonyl groupwith two single bonds to other carbonatoms.In systematic chemicalnomenclature, ketone names endwith the suffix -one.Examples arepropanone (acetone), CH
3COCH
3, andbutanone (methyl ethyl ketone),CH
3COC
2H
5. Ketones can be made byoxidizing secondary alcohols to convertthe C–OH group to C=O.Certainketones form addition compoundswith sodium hydrogensulphate(IV)(sodium hydrogensulphite). They alsoform addition compounds with hydrogencyanide to give cyanohydrinsand with alcohols to giveketals.They undergo condensationreactions to yield oximes, hydrazones,phenylhydrazones, and semicarbazones.These are reactions thatthey share with aldehydes. Unlikealdehydes, they do not affectFehling’s solution or Tollens reagentand do not easily oxidize.Strong oxidizingagents produce a mixture ofcarboxylic acids; butanone, for example,gives ethanoic and propanoicacids.
