Trying to think of a molecule tonight, my friend suggested "pick an ugly one no one wants anymore...a clearance rack molecule." I immediately went to chlorinated solvents. They're in the backwater now, right? Carbon tetrachloride sure has a bad rep. I figured most of the organochlorides, except for the ubiquitous lab solvents, would, too. I was wrong.
Perchloroethylene, or "perc," is a dry cleaning solvent. A few years back, I was surprised to learn that the non-chemistry nerds in my family knew of it, and I came to learn that grandpa owned a dry-cleaning shop back in the day, where he, in fact, used the stuff.
But that was the old days, right? Surely we aren't bathing our clothes in the stuff anymore? It's "a clearance rack molecule," right? Apparently not:
Perchloroethylene ("perc") has long been recognized as an effective dry cleaning solvent and today it is by far the most commonly used solvent in dry cleaning shops.
Perchloroethylene: it has to work really well if it's still around. Any comments from anyone familiar with dry cleaning chemistry?
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Actually Grandpa used a supposedly less toxic solvent from DuPont pointing out it's merits over Perc to any one who would listen. Reading your blog brought back memories of buying and using Carbon Tet that we would purchase from Halverson's Stamp Collecting. We would use it as if it were as toxic as water. Odd that in those days that a 10 year old kid could walk in and buy all the Carbon Tet he wanted. Probably didn't hurt us any more than playing with mercury or the lead wheel weights we'd pick up at tire shops to use for fishing weights. Ahhh . . . the good old (and ignorant) days.
Actually [ed: this really is my Dad, whose Dad is the Grandpa to which I refer] carbon tet is probably even more notorious. It may have just been that carbon tet was even more widely used, but it's definitely bad. At one point it even made its way into fire extinguishers - it was one of the earliest (most toxic) Halons.
I'm a chemical engineer working for an engineering consulting company that regularly deals with groundwater contamination, and let me tell you, there is no better way for you (generic "you") to support my company's livelihood than to continue to use perchloroethylene (or trichloroethylene) for dry cleaning. Whenever it leaks from any given tank into the soil underneath your business, I can guarantee you that 10 years later, someone will be paying my company or someone similar to design a system to clean up all the contaminated soil present. So, it may smell like (chlorinated solvent) to you, but it smells like money to me.
Just goes to show you that not all chlorinated solvents are equal. Physical properties matter. The vinylic C-Cl bond is much stronger than the C-Cl in freons, and so unlike (saturated) chlorofluorocarbons, chlorinated ethylenes are not good radical sources, and therefore are not ozone depleters to the same extent. Of course, the olefin, itself, is reactive with ozone, but not nearly as reactive as radicals.
That is why tetrachloroethylene is still being allowed for use in commercial application.
Halogenated hydrocarbon-contaminated aquifer plumes are remediated at obscene expense. The simple solution is to locate the distal edge, dig a trench in front, then fill the elongated hole with coarse sand and shredded scrap iron. Enviro-whinerism upstream is reduced to nothing downstream. (Don't activate the metal with mercury - iron doesn't amalgamate.)
Methy tert-butyl ether, Enviro-whiner fuel oxygenate darling and EPA priority carcinogen, is forever. Gee - I wonder how it got into our drinking water? An advocate makes virtue of failure. The worse the cure the better the treatment - and the more that is required.
Naddio, thanks for the reminder of the good ol days. Listening to all the alties you would think that people were never exposed to toxic chemicals until recent times.
Apparently the latest fad in dry cleaning is to use liquid CO2: http://www.co2olclean.com/process.html
Carbon Tet was also used as a cattle drench. I remember making it up in large 44 gallon drums out the back of a country pharmacy in my youth.
I believe carbon tet (and sometimes benzene) are still used as spot removers by drycleaners. tricholoroethylene (TCE) was only used for a few years in the sixties and was supplanted by perc (PCE) and stoddard solvent (petroleum distillate). TCE use has been fairly dramatically reduced in the last decade but PCE is still be used a great deal. It has the same toxicological properties as TCE (the differences are mainly in the kinetics) and there is abundant evidence that PCE is a human carcinogen. It is an ackknowledged animal carcinogen (IARC 2B).
Both are dechloriinated by anaerobes and wind up as vinyl chloride in the groundwater eventually. VC is a known human carcinogen.EPA has been dragging its feet on this one for a decade. It's time to phase out both TCE and PCE. They are among the top most prevalent groundwater contaminants in the US, as Uncle Al, notes and there is no place for them today.
My roommate, when he was moving out, cleaned his oil stains from the garage using perchloroethylene, not 3 days after you posted this article. I wouldn't have known what it was, otherwise.
The USAF used perc for cleaning airplanes as recently as 1988. Used spray down the entire thing - thing being a C-5 Galaxy - before we brought it into the hangar. Don't buy land near a Air Force Base, nor drink the water.
I remember using the stuff in Incirlik AB in Turkey and wondering about if it was as safe as "they" claimed. Being a chickensh!t electrician, I wore a hazmat suit when cleaning parts (generators and constant speed drives).
Well, aside for winter coats about every 3 years, I never send anything to the drycleaner. I guess it is one of the perks (haha) of being a chemist. I work in jeans and t-shirts, not fancy suits requiring dry-cleaning. The stupid thing is, if some clothes were made properly, they would not need dry cleaning (pre-washing of fabrics before assembly, using better quality lining and padding materials). I have lots of friends wearing suits to work who dry-clean all their shirts out of pure laziness (to avoid ironing).
I would like to ask you for additional info about perchloethylen. Are any web based info sources about this chemical? I woul need some info about cleaning possibilities. For example i am using it for scleaning metal scrap, but need some other cleaning chemical, more environmental friendly. Thanks. Great blog btw.
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