Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 7, pp. 1128−1132.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © O.V. Lefedova, M.P. Nemtseva, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 7, pp. 1163−1167.
AND POLYMERIC MATERIALS
and Its Hydrogenation Products
in Polystyrene Stabilization
O. V. Lefedova and M. P. Nemtseva
Ivanovo State University of Chemical Technology, Ivanovo, Russia
Received August 19, 2011
Abstract—Liquid-phase hydrogenation of 2-(2-hydroxy-5-methylphenyl)benzotriazole on Raney nickel with the
formation of tetrahydro-2-(2-hydroxy-5-methylphenyl)benzotriazole exhibiting photostabilizing properties was
studied. Enhancement of the resistance of polystyrene items to visible and UV radiation was examined.
Thanks to high photostabilizing activity and lack
of carcinogenic effect, hydroxy-substituted 2H-benzo-
triazoles are widely used as effective photostabilizers
and UV absorbers for various materials. A particular
place among polymer photostabilizers is occupied
by Benazol P, or 2-(2-hydroxy-5-methylphenyl)
benzotriazole (I) [1–5]. For example, benzotriazole I
and its derivatives are preferred in photostabilization of
The mechanism of the light-protecting effect of
substituted 2Н-hydrobenzotriazoles is associated with
excitation of molecules upon their interaction with
a light quantum. As a result of intramolecular proton
transfer from the hydroxy group to the benzotriazole
ring, the quinoid structure of the molecule transforms
into the benzoid structure. The subsequent thermal
isomerization leads to the initial quinoid o-hydroxy
structure, which has the minimal energy. Thus, the
mechanism of the light-protecting effect of substituted
2H-hydroxybenzotriazoles is determined by rapid
tautomeric transformations of molecules in the excited
A promising method for preparing compound
I and its analogs is catalytic hydrogenation of the
corresponding 2-nitro-2'-hydroxyazobenzenes on
transition metal catalysts in various solvents. Liquid-
phase hydrogenation of 2-nitro-2'-hydroxy-5'-
methylazobenzene on Raney nickel catalyst with the
aim to prepare benzotriazole I is a complex multistep
process involving formation of a large number of
intermediates and by-products [6–10]. A distinctive
feature of this process is that it involves simultaneously
both homogeneous and heterogeneous-catalytic steps
of transformation of the initial nitro azo compound and
intermediate products of its hydrogenation.
The sequence of transformations of substituted
benzotriazole in its deep hydrogenation is shown in
the scheme. Addition of 2 mol of H
I yields tetrahydro-2-(2-hydroxy-5-methylphenyl)
benzotriazole II. The subsequent reaction of II with
2 mol of H
yields the ﬁ nal product, octahydro-2-(2-
hydroxy-5-methylphenyl)benzotriazole III. We have
synthesized these compounds, conﬁ rmed their structures,
and determined their physicochemical constants [6–8].
The goal of this study was to assess the possibility
of using hydrogenation products of I as polystyrene
stabilizers exhibiting maximal photostabilizing activity.
As a catalyst we used Raney nickel prepared from
nickel–aluminum alloy with a particle radius of 4.8 μm.
To obtain the active catalyst, the alloy was treated with
a 7.5 M aqueous NaOH solution, after which it was