Sweet Problem Bitter Solution
Akbar once demanded a single answer to three questions. “Why did the horse stumble or the chapatti burn or betel leaves rot?” Birbal, the wise man, answered, “When not moved around”. Likewise, consider these three questions, “How to prevent sale of industrial sugar in the food market?”, “How to prevent pigs nibbling and injuring other pigs’ tails?”, and “How to prevent deers nibbling saplings planted in a jungle?” A modern day chemist’s single answer would be – “Make it bitter”. That’s true.
Pigs in a sty nibble at the neighbor’s tail, causing injury, infection and a loss of quantity and quality of meat. A bitter substance applied to the tails prevents nibbling. Remember how mothers eliminate their child’s thumb sucking? But how does one render tree shoots in jungles bitter, long enough, despite natural elements, and animals? And the idea of making sugar bitter is simply outlandish. Yet it has been done.
So what is that substance, which will render even sugar bitter, or stay active for weeks on end in a jungle? Scientists in M/s T&H Smith of Edinburgh, UK discovered one such substance, in 1958, by accident. They named it Bitrex. The story of its discovery is interesting as well as illustrative of how the industrial research world ticks. But first, we must understand the scenario of how it began.
Lignocaine or lidocaine (C14H22N2O) was an established local anesthetic in the early fifties. It is used even today. Initially it was extracted from natural materials, but chemists and engineers soon developed a process for synthetic Lignocaine. In a research program to enhance its efficacy, Dr. W. Barnes synthesized various soluble derivatives Lignocaine, and sent them for testing anesthetic properties. One of the derivatives was Lignocaine benzyl chloride.
Lignocaine benzyl chloride did not score well as a local anesthetic. But scientists soon discovered it was extremely bitter. An eternal ground rule of every laboratory, prohibits tasting of any new substance developed. But bitterness of this new substance was obvious. As soon as the lid was taken off the bottle, a nasty bitterness would pervade the whole laboratory.
As luck would have it, this company was in the business of manufacturing Brucine, the bitterest substance known until then. Humans can detect the presence of just one gram of Brucine in 220 L of water, by the bitter taste. In those days, Brucine was used to denature industrial ethyl alcohol, to render it bitter and unfit for drinking. But Brucine is also very poisonous. A dose of only half a gram injected into blood will kill an adult human. So Brucine, as well as alcohol containing it, had to be handled very carefully. More importantly, availability of brucine was linked to consumption of its co-product Strychnine. Strychnine is half as bitter but twice as toxic as Brucine. Both Strychnine and Brucine were extracted from Nux Vomica seeds imported from India. If the demands for Brucine and strychnine did not match the production, the whole economics is affected. That is another facet of the story.
In those days Strychnine was traditionally used for poisoning rabbits to control their population, as it happened to be the most worrisome pest for agriculture. It was a major use of Strychnine. In the early fifties, zoologists discovered that rabbit population in South America is affected by a disease called myxomatosis. To achieve a natural control the rabbit population, biologists introduced the disease into the rabbits in Europe and Australia. That worked, and the demand for strychnine was reduced dramatically. Brucine was in demand, but with reduced production of Strychnine, the supply of Brucine was adversely affected. The newly discovered synthetic bitter substance, offered a commercial solution to a host of problems. Unlike Brucine, its availability was not linked to another product like Strychnine. If the new substance was at least as bitter as Brucine, and less toxic, then it can easily replace Brucine as a denaturant for alcohol.
The company went into a high gear research plan. What they discovered far exceeded their expectations. They found that like lignocaine benzyl chloride, the benzyl benzoate salt of lignocaine is equally bitter and has better physical properties. Lignocaine benzyl benzoate was variously called Denatonium benzoate or Bitrex. Bitrex, clearly, was the bitterest substance known to man, even bitter than Brucine.
If 1 g of Brucine could be just detected when mixed in 130 L of water, then 1 g of Bitrex could be detected in 100 000 L water. 10 000 L of water containing 1 g of Bitrex was impossible to drink. Thus, Bitrex was a more effective deterrent in preventing drinking of industrial alcohol, at even lower concentrations of denaturant. This also reduced the interference of the denaturant in some reactions.
Bitrex is disliked by animals as well. However, concentrations required were a little higher than the concentrations adequate for deterring humans.
Unlike Brucine, Bitrex was far less toxic. It was not an irritant and did not cause any mutagenic changes in living organisms.
Bitrex was extremely stable, unlike Brucine. It remained active even when heated to 140 °C and in presence of strong acids and alkalis. It was not affected by light. Substances rendered bitter by Bitrex retained their bitterness for years.
Over the years, it has been used in a number of ways, demonstrating the human ingenuity.
Today Bitrex is widely used as denaturant, all over the world, in industrial as well as consumer products (such as windscreen washing liquids) employing ethyl alcohol. As mentioned at the beginning, Bitrex was used as denaturant for sugar imported for industrial use in Britain, in the sixties of last century. Rendering the sugar unfit for personal use enabled the government to tax it at a lower rate. In USA as well as South America Bitrex has been used for denaturing of vegetable oils or tallow reserved for industrial use.
Formulations of Bitrex have been used on pigs, horses, deer, cats, dogs, birds, hedgehogs, at somewhat higher concentrations than for humans. Bitrex in a greasy base has been used for preventing cribbing of stalls by horses, as well as the cannibalism in pigs, or for preventing deer nibbling young shoots on trees, cited earlier.
It also serves as a constituent of placebo to give it a drug-like taste.
By far the noblest use of Bitrex is in toxic consumer products, so as to prevent their accidental consumption, by unsuspecting consumers and especially children. This includes products such as cleaning liquids, detergents, shampoos, hair sprays, insecticides, baits for trapping household pests, biocides, household liquid fuels etc. Bitrex is used in such products to render them so unpalatable that even an unsuspecting abuser, and particularly children, will not be able to consume any significant quantity to pose health hazard. Similarly Bitrex is used in nail paint formulations to prevent nail biting.
Efficacy of Bitrex has been tested on children, the largest target group that is expected to be protected by its use as an aversive agent. Results were interesting. Children invariably disliked the taste so much so that most children do not taste a Bitrex containing product a second time. No child has dared taste it a third time in trials, anytime!
We should be grateful to these chemists and engineers inventing and manufacturing the bitterest substance on earth and employing it for such a noble cause of preventing accidental poisoning of customers in general and children in particular !
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