home applications more details science links & more legal

Scientific Data

Azo Initiator

Chemically, 2,2'-Azobis-(Amidinopropane) Dihydrochloride belongs to the class of aliphatic azo compounds of the general structure (Fig.1):

Fig. 1. Structure of aliphatic Azo compounds

Two tertiary Carbon atoms are attached to a group of two Nitrogen atoms whith a double bond. As a function of the residues on both carbon atoms, the molecular structure may be more or less thermally stable. In the case of the substance represented, the residues at the carbon atoms are symmetrical, i.e. R1 =R2, R3 = R4, and R5 = R6 (see Fig. 2). Furthermore, each carbon has two identical residues (methyl groups) so that R1 =R3, R2 = R4 and, in consequence, stereoisomerism of the molecule is limited to the Nitrogens (E or Z) only. This stereoisomerism is without practical relevance, however.

Aliphatic azo compounds most often are thermally unstable. They easily decompose liberating Nitrogen gas and 2 radical fragments which react further with the microenvironment, a property which is used for initiation of various radical processes.

Further properties of the azo compound - e.g. solubility, stability - are defined and may be designed by the different residues R.

Basic Data


2,2'-Azobis(2-methylpropionamidine) dihydrochloride
2,2'-Azobis(2-amidinopropane) dihydrochloride
2,2[-Azobis(2-methylpropionamidine) dihydrochloride
2,2'-Azobis(isobutyramidine) dihydrochlorid
2,2'-Azobis(2-amidinopropane) dihydrochloride
2,2'-Azobis(2-methylpropionamidine) dihydrochloride


Fig. 2. Structure of 2,2'-Azobis(amidinopropane) Dihydrochloride

Basic properties

[ 2997-92-4 ]

EINECS code:

sum formula:

molecular mass:

melting point:
163 - 170 °C

solubility, org. solvents:
almost insoluble in most organic solvents

solubility, water:
very high ( > 20 g/l at 20 °C)

Half Life Values

The most important characteristic of a polymerization initiator is the speed of formation of radicals. As a general measure, the terminus Half Life is used. The Half Life is defined as the time required for half of the molecules of a given quantity of initiator to decompose, and it is closely related to temperature as it follows kinetics under Arrhenius equation.

Half Life at different pH Values

In contrast to other Azo initiators with neutral structure, 2,2'-Azobis-(amidinopropane) Dihydrochloride consists of protonated substructures at "normal" ph Values. Part of the decomposition kinetics may be explained by electrostatic repulsion between positively charged centers. As a basic environment may influence the protonation of the molecule, the half life behaviour is partly dependent on the pH.

Kinetic Constant of Decomposition and Half Life vs. pH at 70°C (158°F)


K [10-4 s-4]

Half life [min]










In addition, at ph values of 9,5 and above hydrolysis of the amidino group may have negative impact on the decomposition rate.

© 2002, 2003 by Dr. W. M. Doerner