MELAMINE PREPARATION P. P. MCCLELLAN American Cyanamid Company, Stamford, COM. N
M
ELAMINE is one of the most recent additions to the field of important industrial chemicals. Less than two years ago it could be obtained only as a rare chemical at a nominal price of about $40 a pound. The pace of technology has been so rapid that nom it can be purchased by the ton for about one per cent of its previous price. It has shown great promise in the field of amino plastics owing to its remarkable stability to heat and light; and its reactions lead to the belief that it will become an increasingly useful basic material for synthesis. Melamine is a member of a class of compounds known as the triazines. Two other members of this class, cyanuric acid and cyanuric chloride, are probably better known than any of the others. Their structural relations to melamine, ammeline, and ammelide may best be shown graphically:
&
N
NC/ I
NHz Melamine CsHeNs NH2
cI
h-
cII
cI
/\/>
PU-
N
N
\.,-“,
I
N
N
I I /I NHz-C C C-NHz \ / \ / S
bH Cyanuric acid
Cl Cyanuric chloride
N
IbH* Melamine Melon is thought to be a condensed ring or chain of melem groups. The similarity between melon and graphite may be particularly noted in the condensed ring system. The com-
__
II I N \/
N
I
II
N
be considered as the whole of the melem structure with its three fused rings:
N
”2
NHz I
AH
Ammelide
Ammeline
HX
Melamine may also be considered as the trimer of cyanamide, CH2N2,of which dicyandiamide is the dimer. These relations may be shown pictorially by the commonly accepted structural formulas: hT
N=C
I
kH
\/
N i 4
T\”
I
NHz Dicyandiamide
NzC I
hH2 Cyanamide
NC/
I NHZ
Melamine
It is likewise structurally related to the compounds melam, melem, and melon through the loss of ammonia. Although their true structures become increasingly vague with increasing loss of ammonia, Redemann and Lucas (2s)suggested that the following structures best describe the molecular pictures of melam and melem:
NHi
A
NH
n n
NH NHz Melon CisHeKzT
I n 1834 Liebig (28) heated a mixture of potassium thiocyanate and ammonium chloride together in a retort in much the same way as Wohler six years earlier had conducted his classic experiment when he synthesized urea for the first time from potassium cyanate and ammonium chloride. Liebig obtained from his fusion mixture a residue which he called “melam”. By heating this residue with a dilute solution of caustic for several days, he obtained a material that crystallized out when the solution was cooled. His analysis showed that it contained only carbon, hydrogen, and nitrogen, and behaved as a weak base. He decided to call this new base “melamine” because he concluded that it had been formed by the action of alkali on melam but, as will be shown later, this was not true; the melamine was present before the treatment with caustic. Investigation of melamine has been sporadic during the past century, and only in the last five or six years has any
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