formaldehyde - Sciencemadness Dot Org

202
FORMALDEHYDE
In the case of ethylenediamiue, BischofP obtained a crystalline product
(m.p. 196 C C) whose molecular weight indicated it to be a dimer of the unit
shown in the type reaction above. It is believed to have the following
structural formula;
H.C—X— CH2—N—CHs
! I I
I I I
HaC—N—CHi—N—CHa
The products from tri- and tetramethylenediamines are high-boiling liquids,
whereas the product from pentamethylenediamine is a solid** 10& .
Under acidic conditions, amines react with formaldehyde to form compounds
which, on neutralization, give those methyleaeamines which would
be normally expected from the reaction in alkaline media. However,
according to Werner 128 , there is evidence that in the case of primary amines
methyleneamines are not formed in the acidic mixture, but that dissociated
salts of methyleneimines are;
CHsXHa-HCI 4- CH20{aq) -* CHS:NCH3(HC1) + H20
With secondary amines, salts of tetraalkyl methylenediamines are obtained,
the reaction being practically unaffected by the presence of aeid 128 .
On heating amines, diamines, or their salts with excess formaldehyde}
secondary or tertian - methyl alkylamines are formed; they may be isolated
on treatment of the reaction mixture with caustic alkali 34 - 35 . Reactions of
this type are involved in the preparation of trimethylamine from formaldehyde
and ammonium chloride (pages 121-122). As has been previously
pointed out, a portion of the formaldehyde serves as a reducing agent and is
converted to formic acid or carbon dioxide. Reactions take place slowly
and incompletely in the neighborhood of 100 °C, but are completed in a few
hours when carried out under pressure at 120-160°C. Reactions of this
type are also obtained when formaldehyde is employed in polymeric form,
e.g., paraformaldehyde. The fact that hydrogenation catalysts are
claimed to be of value in the preparation of tertiary methylamines by heating
secondary amines with paraformaldehyde 54 may indicate that hydrogen
is actually liberated in the course of the reaction, which is in some respects
quite similar to the crossed Cannizzaro reaction.
Tertiary amines are obtained in yields of better than 80 per cent theoretical
when simple aliphatic amines are wanned with formaldehyde and formic
acid 17 . Under these conditions formic acid acts as the reducing agent.
The reduction of the cyclic trialkyl trimethylenetriamines with zinc and
hydrochloric acid, which has already been noted, is indicative of the ease
with which products of this type are hydrogenated. That methylolamines