Skeletal Formulas and the Export of Occupational and Environmental Hazards


Whether it’s a scientific discipline, plumbing or a sport, every specialised field has its own terminology—words that don’t often enter into everyday vocabulary but which are used without a blink among specialists. The term for such in-crowd words and expressions is jargon. But in many subject areas,  jargon can also come in the form of images. Even the rare person who remembers their introductory chemistry courses would still be taken aback by the following skeletal formula:

the skeletal structure of ethanol

Uniquitous in online data bases (Chem Spider, Merck Index or CRC handbook), a skeletal formula is what I call image-jargon. The common atom in organic compounds, carbon, is often symbolised by an angle or a corner. Since it is assumed that the person looking at the structure knows that, except in radicals, carbon will make four bonds, some of the hydrogen atoms are also hidden. For example in the above skeletal formula of ethanol, the alcohol found in wine, beer and spirits, there is one angle representing a carbon and that “hidden” carbon is bonded to an OH group and to a methyl group (CH3). That’s only two bonds so far, so there have two be two more hydrogens for a total of six. The molecular formula of ethanol represented by that skeletal structure is C2H6O. In other words the above skeletal structure is equivalent to this three dimensional model of the molecule:

C2H6O or ethanol

For compounds containing only carbon, hydrogen and /or oxygen and/or nitrogen and/or halogens, there’s a nice formula  we can use to verify that we are putting in the right number of hydrogens. (If you think the conditions are restrictive, compounds with the mentioned elements include the majority of carbohydrates, fats, alkaloids, amino acids  and all terpenes, esters,  and petroleum products—-literally millions of known compounds in total

C + 1 – (H- N+ X)/2  = degree of unsaturation (d.u.),

where C = number of carbons; H = number of carbons, N = nitrogens and X = number of halogens such as fluorine, chlorine, bromine and iodine. Notice that the number of oxygen atoms have no impact on the degree of unsaturation. .

What raises the degree of unsaturation from zero is any “ring” system (closed loop structure; it could be triangular, hexagonal, etc) or a double bond, which looks like an equal sign. A triple bond raises the d.u. by two.

So for our ethanol structure, there are no such double bonds or ring structures, so d.u. = 0. Since C =2, then

2 + 1 – (H-0 + 0)/2  = 0

Solving for H, we obtain H = 6

Let’s look at one more:

benzidine, a group I carcinogen

Here we have 12 angles (6 in each hexagon) for a total of 12 carbon atoms. The degree of saturation is raised to 8 by the presence of 6 double bonds and two hexagons.

C + 1 – (H-N + X)/2  = degree of unsaturation

12 + 1 – (H-2 + 0)/2  = 8

H = 12, which implies that 8 hydrogens are hidden by the skeletal formula, one at each carbon(corner) to give each carbon four bonds.

Benzidine is no longer sold in the United States, Canada or Europe. This has been the case since the mid-1970s. It was mainly used in the production of dyes found in cloth paper and leather. It is a class 1 carcinogen, increasing the risk of bladder cancer in humans, especially for who worked in an occupation that exposed them to such dyes.

Unfortunately that is not the end of the story. There are still benzidine derivative compounds, which are not group I carcinogens but  group 2 substances, which probably causes cancer in humans. One such compound is 3,3′-dichlorobenzidine.

3,3-dichlorobenzidine, a group II carcinogen

Although it is not made here in Canada, we import 100 tons of it every year from Asia because the compound is used as an intermediate to make yellow to yellow green pigments for printing inks, textiles, paints, plastics and crayons. Health and Welfare Canada is not worried about trace amounts of the substance because of the concentrations involved and because the compound is not used in any edible products. Unfortunately no one has ever gathered evidence for the combined effects of the cacophony of trace carcinogens we are exposed to in modern life. Moreover, especially since safety standards for workers are typically lower in Asia, it is unfair to them if we persist in consuming such large quantities of the compound. Like all aromatic amines, 3,3′-dichlorobenzidine is easily absorbed through the skin and lungs. According to the Center for Disease Control and Prevention,

Employees engaged in handling operations involving compounds in the list below(which includes 3,3′-dichlorobenzidine)  must be provided with, and required to wear and use, a half-mask filter-type respirator(SOHA standards) for dusts, mists, and fumes.  A respirator affording higher levels of protection than this respirator may be substituted.

Even in the United States , the OSHA Respirator Standard has been known to be violated by almost half of companies surveyed in 2000 to 2002. More recently a significant number of violations persisted. One could only imagine what safety practices are like in India, which, worldwide,  has the most chemical plants , specifically 6,  producing this substance.

Coincidentally, this morning a few hours after I paused writign this article, The Current on CBC interviewed a medical doctor, Paul David Blanc, who was discussing a parallel situation involving carbon disulfide (CS2). This reagent is used in the second last step in the production of  viscose, also known as rayon. According to WHO, for every kilogram of viscose produced, about 20-30 g of carbon disulfide and 4-6 g of hydrogen sulfide are emitted . The highly volatile carbon disulfide, if not diverted, fills factory workrooms with fumes that can have long term effects such as depression, mental illness and suicide. Other side-effects include blindness, impotency, and malfunctions of the vascular system and other organs. Rayon is no longer produced in North America after claiming many victims in the late 19th and early 20th century. In Europe the vapours are recycled, keeping levels safer for workers. But such is not always the case in Bangladesh and elsewhere in Asia. Yet we import these goods, ignoring the consequences suffered by producers.
Rayon is  not the only commercial product made with carbon disulfide. A more complete list includes cellophane, sponges, sausage casings, pesticides and carbon tetrachloride. In one of the most unethical examples of greenwashing, marketers label “bamboo fabrics” as being “green”. But the manufacture of these products again relies on carbon disulfide  and takes place in China where laws  protecting labourers and the environment from  CS2’s toxicity are either less stringent or non-existent.

The recent election in the United States was won by Donald Trump, who among other things, exploited a populist resentment of free trade. But the focus was entirely on the loss of American jobs. It’s not a coincidence that the anti-environmental winning candidate did not use imported dyes and rayon as part of his argument. Given that automation is also a cause of job-loss in the Western world, the solution is not to take manufacturing jobs away from Asian countries. Instead what’s needed is to incorporate occupational and environmental regulations into the free trade arguments. Otherwise the Western world will continue to export occupational hazards and pollution to Asia.

Other Sources:

Fake Silk The Lethal History of Viscose Rayon. Paul David Blanc. Yale University Press. 2016. 325 pp.