The systematic name for an aldehyde is obtained from the parent alkane by removing the final -e and adding -al.
For ketones the final -e is replaced by -one, and a number indicates the position of the carbonyl group wherever necessary. The carbon chain in ketones is numbered such that the carbonyl carbon gets the lowest possible number.
In aldehyde the carbonyl group is always at the end of the chain and is always assumed to be carbon number 1. The positions of the other substituents are specified by numbers as usual. The following examples illustrates these principles.
The names in parentheses are common names that are used much more often than the systematic names.
An alternative system for naming ketones specifies the substituents attached to the C=C group. For example, the compound 2-butanone is used in the system as described.
However this molecule also can be named methyl ethyl ketone and is commonly referred to in industry as MEK (methyl ethyl ketone).
Aldehyde are oxidized to carboxylic acids by a variety of oxidizing agents, including potassium dichromate. Aldehyde are also oxidized to carboxylic acids by the oxygen in the air.
Ketones in contrast resist oxidation by most oxidizing agents, including potassium dichromate and molecular oxygen.
The fact that aldehydes are so easy to oxidize and ketone does not. To distinguish between these types of compounds simple chemical tests are carried out.
Suppose that we have a compound we know is either an aldehyde or a ketone. To determine which it is we can treat the compound with a mild oxidizing agent. If it can be oxidized it is a aldehyde otherwise its a ketone. One reagent which has been used for this purpose is Tollens reagent.
Aldehydes are reduced to primary alcohols and ketones are reduced to secondary alcohols.
The reduction of a C = O double bond under these conditions is slower than the reduction of a C = C double bond. Thus if the same molecule contains both C = O and C = C double bonds, the C = C double bond is reduced first.
1. By ozonolysis of alkenes
Alkenes react with ozone to form ozonides which on subsequent reductive cleavage with zinc dust and water or H2/Pd give aldehydes, Ketones or a mixture of both depending on the substitution pattern of the alkene.
Zinc dust removes H2O2 formed, which otherwise can further oxidize the aldehyde formed to acids.
Using a suitable alkene, the desired aldehyde or ketone can be formed.
2. By hydration of alkynes
Ethynes adds water in the presence of H2SO4 and HgSO4 to give acetaldehyde.
Hydration of other alkynes under similar condition gives ketones.
3. By oxidation of methylbenzenes
Oxidation of an aromatic compound leaving a methyl group at the benzene ring with CrO3 in the presence of acetic anhydride followed by hydrolysis gives the corresponding benzaldehyde.
Further oxidation of the benzaldehyde to benzoic acid is prevented as the aldehyde is trapped by acetic anhydride as a non-oxidisable benzylidene diacetate derivative. This reaction is called the Etard reaction.
4. From Nitriles
Partial reduction of nitriles with acidified stannous chloride SnCl2/HCl at room temperature gives aldehydes. In the first step imine hydrochloride is obtained which on subsequent hydrolysis with boiled water gives aldehyde. This specific type of reduction of nitriles is called Stephen's reduction.
SnCl2 + 2HCl $\rightarrow$ SnCl4 + 2 [H]
Similarly benzonitrile gives benzaldehyde.
Ketones are obtained when Grignard's reagent add on to nitriles. The imine salt intermediate that is formed on hydrolysis gives ketone.