Pyrimidine
January 21, 2010
Pyrimidine is an aromatic organic compound which is heterocyclic and similar to benzene and pyridine. It contains two nitrogen atoms at positions 1 and 3 of the six-member ring. It is isomeric with two other forms of diazine.
Pyrimidine can be prepared within the laboratory by organic synthesis method. One of the methods is the “classic Biginelli reaction”. Another method is by reaction of certain amides with carbonitriles under electrophilic activation of the amide with 2-chloro-pyridine and trifluoromethanesulfonic anhydride. Many other methods rely on condensation of carbonyls with amines for instance the synthesis of 2-Thio-6-methyluracil from thiourea and ethyl acetoacetate or the synthesis of 4-methylpyrimidine with 4, 4-dimethoxy-2-butanone and formamide.
Pyrimidine is also found in meteorites, although scientists still do not know its origin, Pyrimidine also photolyticly decomposes into Uracil under UV light. Pyrimidine has many properties in common with pyridine, as the number of nitrogen atoms in the ring increases the ring pi electrons become less energetic and electrophilic aromatic substitution gets more difficult while nucleophilic aromatic substitution gets easier. An example of the last reaction type is the displacement of the amino group in 2-aminopyrimidine by chlorine and its reverse. Reduction in resonance stabilization of pyrimidine may lead to addition and ring cleavage reactions rather than substitutions. One such manifestation is observed in the Dimroth rearrangement. Purines and pyrimidine make up the two groups of nitrogenous bases, including the two groups of nucleotide bases. Two of the four deoxyribonucleotides and two of the four ribonucleotides, the respective building blocks of DNA and RNA, are Purines.
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