Historical Use of Chlorinated Solvents and Their Stabilizing Compounds - Environmental Investigation and Remediation - page 44

TABLE 1.22
Antioxidant Compounds Used in Chlorinated Solvents (Partial List)

Solvent and List of Antioxidant
Compounds Quantity (vol%) a References

Methylene chloride
2-Methyl-2-butene

0.5 Irani (1977)

Phenol 0.05-0.5 Daras (1960), U.N. Environment Programme

(UNEP) (1984)

Thymol 0.001-0.5 Pray and Chisholm (1960)

Cresol Present in vapors Ramos (1974)

Stabilized trichloroethylene
Thymol

0.001-0.5, 0.28 Shepherd (1962), World Health Organization

(1985), Pray and Chisholm (1960)

p - t -Amyl phenol 1-5 Shepherd (1962), Fullhart and Swalheim

(1962), Watson and Rapp (1959)

Phenol 0.001-0.5 Pray and Chisholm (1960)

(0.05-0.5 g/L)

Pyrrole Smallwood (1993)

n -Methyl pyrrole 0.022-0.028 Copelin (1959), Shepherd (1962), Tarrer et al.

(1989), Starks (1957), OEHHA (1999)

1-Ethoxy-2-imino-ethane 0.01-0.02 Smallwood (1993)

Perchloroethylene
2,6-di- tert -butyl- p -cresol b 30 ppm, 80 ppm Dempf et al. (1977), Howell and Tarrer (1994)

Thymol 0.01% wt/wt Reynolds and Prasad (1982)

Methyl chloroform
Resorcinol 0.0001-1 World Health Organization (1990)

Except as noted.

a

Also known as Ionol™.

b

patent literature is cited where a particular patent discloses stabilizer compositions in use at the time
the patent was issued, but this practice is not intended to imply that the stabilizers claimed in the patent
are present in the solvent. Patent claims on stabilizer packages are nevertheless useful and informative
as an indirect means of understanding the empirical art of stabilizing solvents. A comprehensive com-
pilation of stabilizers claimed in United States, British, and Canadian patents issued to United States,
British, Canadian, German, Belgian, French, and Italian companies is presented in Appendix 1.

1.2.6.1 Solvent Stabilizer Chemicals
The major solvents have been stabilized with groups of chemicals identii ed as having an inhibiting
effect on the reactions or catalysts that break down solvents. Each chemical added serves a distinct pur-
pose, such as neutralizing acids, supplying an antioxidant, and inhibiting reactions with metal chloride
salts. Finding the right chemicals to perform these tasks was the subject of much research and experi-
mentation. For many years, the nature of the reactions that cause solvent breakdown was not identii ed
or well understood by the industrial chemists whose task it was to prevent these reactions. In 1943, an
inventor wrote in his patent, “The nature of deteriorative changes being unknown, the operative mecha-
nism is also unknown. Stabilizing action must therefore be determined empirically” (Pitman, 1943).
The patent literature shows that industrial chemists understood which classes of compounds had
the capacity to inhibit reactions. These chemists experimented with many candidate compounds