Amide Group
The amides are a group of organic compounds derived from ammonia (NH3). One or more of the hydrogens of the ammonia is replaced with an organic acid group to produce a primary, secondary, or tertiary amide. The simplest form of amide--a primary amide--has the functional group -CONH2 (a double bond exists between the carbon and the oxygen). A secondary amide is produced when two hydrogen atoms are replaced and has a general formula of (RCO)2NH. A tertiary amide has the general formula of (RCO)3N. All amides have the ending -amide as part of their name. There is no distinction made between the three types in their naming.
The amides are generally crystalline solids which can dissolve in alcohol and ether. Amides are hydrolysed to ammonium salts with catalysis by acids or alkalis. This process is the starting point for the manufacture of a number of organic acids. Reaction with nitrous acid yields carboxylic acid directly as a product.Dehydration of amides is brought about by heating with phosphorous pentoxide and the product of this reaction is the alkyl cyanide. If reacted with sodium hydroxide solution and bromine, amides are transformed into the appropriate amines. This reaction is known as the Hofmann degradation after its discoverer, German chemist August von Hofmann (1818-1892). Another way to produce amines from amides is by reduction. This is carried out at a pressure of 250 atmospheres and a temperature of 490°F (250°C). This reduction reaction requires the use of copper oxides, chromium oxides, or lithium aluminum hydride as a catalyst. Halogenation of amides can occur to give the appropriate chloro- or bromoamides.
Amides can be distinguished from most other compounds by boiling with sodium hydroxide solution. After a short delay they give off ammonia. Ammonium salts treated in the same way give off ammonia immediately, and other nitrogen containing compounds yield no ammonia.
Primary amides are prepared by reacting ammonia or amines with acid chlorides, anhydrides, or esters. Secondary and tertiary amides are prepared by reacting primary amides or nitriles with organic acids. Primary amides are weakly basic and can form compounds with metals such as sodium, potassium, mercury, and cadmium, although heavy metal amides can be explosive. Alkylated amides are used in replacement reactions involving ionic reagents, since they are good solvents for this reaction.
The simplest amide is methanamide, HCONH2. This is the only member of the group that is a liquid at standard temperature and pressure (STP). Methanamide is manufactured by reacting carbon monoxide and ammonia together under pressure. Like the other amides, it is a good solvent for a range of organic and inorganic compounds. The amides have elevated melting and boiling points due to the presence of hydrogen bonds.
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