Antioxidant is a substance added in small quantities to hydrocarbons which are
susceptible to oxidation, such as rubbers, plastics, foods, and oils to inhibit
or slow oxidative processes, while being itself oxidized. Antioxidants work in
two different ways. In primary antioxidants (also called free-radical
scavengers), antioxidative activity is implemented by the donation of an
electron or hydrogen atom to a radical derivative. These antioxidants are
usually hindered amines (p-Phenylene diamine, trimethyl dihydroquinolines,
alkylated diphenyl amines) or substituted phenolic compounds with one or more
bulky functional groups such as a tertiary butyl at 2,6 position commonly.
Butylated hydroxytoluene (BHT) is a common example of hindered phenolic
antioxidant. The reaction rate, or carbocation stability, in SN1 mechanism is 3° > 2° > 1° > CH3
(no SN1) so, tertiary alkyl moiety exists in lots of phenolic antioxidant
compounds. Primary antioxidants are free radical scavengers which combine with
peroxy radicals and break autocatalytic cycle. In secondary antioxidants ( also
called peroxide decomposers), activity is implemented by the removal of an
oxidative catalyst and the consequent prevention of the initiation of oxidation.
Examples of peroxide decomposer type of antioxidant are trivalent phosphorous
and divalent sulfurcontaining compound such as sulfides, thiodipropionates and
organophosphites. Synergistic effect is expected when primary antioxidants are
used together with secondary antioxidants as primary antioxidants are not very
effective against the degradation by UV oxidation. Sometimes, chelating agents
are added to scavenge metal impurities which can initiate decomposition.
is used as a secondary stabilizer and antioxidant
in combination with phenolic antioxidant for
polymers (ABS, polypropylene, polyethylene
and polyesters). It is approved to use in food packaging.
It is also used stabilizer in oils, lubricants, sealants, and adhesives.
Mechanisms of antioxidant action: the nature of the
redox behaviour of thiodipropionate esters in polypropylene
DTTDP and DSTDP are all produced by reacting the same intermediate,
thiodipropionitrile (TDPN), with different fatty alcohols. DLTDP
uses lauryl alcohol, DTTDP uses iso-tridecyl alcohol and DSTDP uses
stearyl alcohol. The reaction of TDPN with the alcohols is an esterification
using acid catalysts (hydrochloric acid and sulfuric acid). Water
is removed under vacuum to drive the esterification to completion.
Then the catalyst is neutralized and salts and impurities removed
in a series of filtrations and washes. The molten DLTDP and DSTDP
are converted to solid products by flaking and packaged. The liquid
DTTDP product is drummed. The TDPN intermediate is made by reacting
acrylonitrile and sodium sulfhydrate in aqueous solution. The resulting
aqueous phase is split off, the product phase washed with water
and the remaining TDPN used to make the thioesters. The reactions
all take place in enclosed reactors, thus limiting potential worker
exposure. The DLTDP, DTTDP and DSTDP all have very low vapor pressures
at ambient temperatures so the risk of vapor contact during manufacture
and drumming is relatively low. These chemicals are used by our
customers who add them to variety of plastics such as polyethylene,
polyolefins (mostly polypropylene), and polystyrene. Common use
levels of DLTDP and DSTDP are 0.1 to 0.2 %. The polymers are then
further processed into items such as washing machine agitators,
battery cases, food packaging materials, and household appliances.