Historical Use of Chlorinated Solvents and Their Stabilizing Compounds - Environmental Investigation and Remediation - page 53

The i rst patent to claim 1,4-dioxane as a stabilizer for chlorinated solvents was i led in
1954 by Dow Chemical (Bachtel, 1957). Dow claimed 1,4-dioxane specii cally to inhibit the
reaction between methyl chloroform and aluminum and presented experimental data to show
its effectiveness. Aluminum alloy coupons were scratched with a stylus to strip away the
aluminum oxide surface coating. These were then immersed in unstabilized methyl chloro-
form, which led to immediate solvent breakdown and evolution of a carbonaceous, tarry mass.
Methyl chloroform stabilized with 3.5% 1,4-dioxane remained water white with no visible
reaction when in contact with scratched aluminum alloy coupons. Similar tests showed the
effectiveness of 1,4-dioxane to inhibit the methyl chloroform reaction with aluminum in a
boiling rel ux chamber for 30 days and for storage in black iron drums for 2 months. Inclusion
of sec -butyl alcohol or tert -amyl alcohol, in addition to 1,4-dioxane, prevented discoloration
of the solvent.
Dow Chemical incorporated 1,4-dioxane into its chlorothene line of methyl chloroform
products with the May 1960 introduction of Chlorothene NU.
WAS 1,4-DIOXANE A STABILIZER FOR TRICHLOROETHYLENE?
Petering and Aitchison's (1945) patent claims a variety of oxygen-containing compounds as
stabilizers for chlorinated solvents, and TCE in particular. The patent (U.S. Patent 2,371,645)
clearly lists 1,4-dioxane and even shows its molecular structure as an example of an “inner
ether.” However, the patent recommends propyl ether as a stabilizer for TCE, because it boils
with the solvent, and emphasizes that the selection of the ether or oxide to stabilize TCE should
be predicated upon its ability to distill with the solvent without loss of the stabilizer. In the
claims section, the class of inner ethers is named, but the only compound specii cally claimed
by name is propyl ether. The patent also claims stabilizers that are “volatile with the chlori-
nated solvent” and stabilizers that are “simple aliphatic ethers” (1,4-dioxane is a cyclic ether).
The boiling-point difference between TCE and 1,4-dioxane is 14°C, a smaller difference
than with methyl chloroform and 1,4-dioxane (which have a 26.9°C difference). The large
boiling-point difference and tendency for 1,4-dioxane to partition and remain in the boiling
sump did not prevent its widespread use for methyl chloroform; therefore, the smaller boiling-
point difference would not by itself preclude the use of 1,4-dioxane to stabilize TCE.
In a 1960 patent i led in 1954 and issued to the Diamond Alkali Company of Cleveland,
Ohio, an encyclopedic list of more than 100 compounds for use as stabilizers is provided,
including “dioxan” (Skeeters, 1960b). This patent cites i ve other patents, none of which men-
tion 1,4-dioxane. This patent is for stabilizing perchloroethylene, but the claims are for other
compounds and do not specii cally mention 1,4-dioxane.
A sampling survey of products made by processes that use organic solvents was completed
in Japan in the 1980s. A large number of solvent samples (1179) were collected and analyzed
by gas chromatography. A small amount of 1,4-dioxane was detected as an additive in every
sample that contained methyl chloroform; however, the study does not mention any detections
of 1,4-dioxane in products produced with TCE (Inoue et al., 1983).
At a number of sites with monitoring wells, 1,4-dioxane is found together with TCE where
no methyl chloroform is detected. Collocation of 1,4-dioxane with TCE does not in itself
prove that 1,4-dioxane was a stabilizer for TCE. At many facilities that operated over long
periods of time, several different solvents were used in response to changing environmental
and worker health and safety regulations. For example, in the late 1960s and early 1970s,
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