How not to Go About Preparing Bromine in the Laboratory

How not to go about preparing Bromine in the laboratory:

Background: Some background is necessary here, if for no other reason, then at least to explain how a fourteen year old Indian in 1971 had the keys of a Senior School Chemistry Laboratory in his pocket. Essential additional background on the physical surroundings in which this particular misadventure occurred has been included as well..

First, some history: In the 1960s India’s Prime Minister, Jawaharlal Nehru convinced himself that in order to become self sufficient, it was essential for India not only to grow its manufacturing base, but also to expand the community of scholars engaged in scientific research…that too, not just those dealing with technological advancement but also those engaged in contributing to the natural sciences. This might seem an impossibly naive attitude today, but it must be remembered that in those days, “unbridled capitalism” (as it was called then) was not the only system going around…Stalin’s excesses had been acknowledged by his successors and Nehru and Co. were exploring (if that is the right word) other alternative paths to development. In any event, it is in consonance with these ideals that India’s National Council for Educational Research and Training (NCERT) went on to institute something called the National Science Talent Search Scheme. At its core was a special scholarship valid immediately after school all the way through college and university. It was available only to those who passed a rigorous series of trials (which included a project report together with a series of written tests and a final interview.) This scholarship was not applicable to those entering a Bachelor of Engineering program. It was clearly stated and understood that those selected had to chose to study one of the natural sciences. Make no mistake. It was an elite program: For example, once selected, it was also incumbent on the chosen scholars to travel to a chosen location once every year (all of this at government expense!) for a four-week long summer camp where well-known scientists from all over India would help the scholars complete a small project relating to their field of study.

About the physical and social environs that surround the event: The school where I was, The Lawrence School, Lovedale, is one of India’s better known public schools. It is located in the Nilagiri Hills where it sprawls over several hundred acres of interconnected plateaus all about 7500 feet above sea level. An important by-product of the school’s geography needs to be noted: The day temperatures rarely cross 22 degrees and on the September day in question the air temperature would have been around 18 degrees and water temperature would not have been more than 12 to 14 degrees Celsius. Had I committed my chemical misadventure at any other place in India the higher ambient temperature could well have had far more serious consequences.

About myself, I was one of the class nerds, tall, not at all athletic, not friendless but to an extent asocial, and, much much more at home with Partington’s Inorganic Chemistry and the miscellaneous examples from Loney’s Trigonometry than with cricket and football. My science teachers thought I was an obvious candidate for the scholarship mentioned earlier. All the way from my class 10 and later, I had access to the chemistry laboratory any time I wanted. I merely had to inform my chemistry teacher who would get the lab attendant to open the lab for me.

The senior school (including the science block housing the chemistry laboratory) was on the highest of the plateaus. The junior school (classes 7 and 8) was on an adjacent shelf as it were and perhaps 50 or 60 feet lower. Sixty-seven stone steps separated the senior and junior schools. Parallel to the stairs (simply called “the 67” by everybody) was a storm drain that debouched just a few meters before the outer fencing of the junior school began.

The Idea and the Faulty Reasoning Behind it: Partington and other textbooks on Inorganic Chemistry set down a well known method for preparing chlorine gas by subjecting a mixture of potassium chloride and potassium permanganate in a flat bottom flask to a drip of sulphuric acid via a thistle funnel. The resulting chlorine can be collected in jars as they fill up and used for the formal confirmation of the gas’s physical and chemical properties. Over a period of time in 1971, I idly thumbed through Partington and a whole bunch of other chemistry texts from the school library for a description of a parallel method for the preparation of bromine by substituting the potassium chloride mentioned above with potassium bromide instead. Surely it was a legitimate method of preparation? I searched, as they say, high and low but found nothing. I found that most puzzling. After all, I reasoned (wrongly as iy turns out!), that since bromine is less reactive than chlorine (that much is true…) the reaction as I envisaged it, would result in the preparation of bromine in a far more benign manner than the former reaction generated chlorine. (As they comment on chess moves: ??).

Here’s the thing: As anyone with a knowledge of high school chemistry would have pointed out, my inference was completely faulty. The correct inference on my part should have been that since bromine is far less reactive than chlorine, it would be that much more easily separated from its salts, thereby concluding that the reaction would be more vigorous. Another inference, equally correct, would have been that if we assume that hydrochloric (HCl) and hydrobromic acid (HBr) were transient intermediary products/reactants within the total reaction processes, then HBr would surely be more reactive than HCl, not less. Had I followed through my thoughts along these lines, I wouldn’t have dreamed of going through with the experiment.

In fact, this was not the only error on my part. A far more serious problem was a factual inaccuracy, a misreading on my part that lead to my arranging the apparatus for my experiment for preparing a liquid/gas that boiled at 58.8 degrees Fahrenheit and not at 58.8 degrees Celsius which is the actual boiling point of elemental bromine! (Just checked on the net.)

In any case, months passed by without my “checking the fine print” and I was determined that while I was working on my project for the scholarship (some stuff dealing with boron and silicon compounds of which I remember precious little) I would also, at some point, prepare bromine by dripping sulphuric acid on a mixture of potassium permanganate and some bromide…you know…just to show everyone that it was possible to do it this way! This event, when it finally did occur, happened completely differently from how I’d imagined it would.

The Event: It was around 3:30 in the afternoon some September day in 1971. It had been a really boring day. I was in the lab and at one end I had, in a crucible, converted boric acid to boron trioxide by the simple act of subjecting the boric acid to consistent heat. I had then taken a length of magnesium ribbon, cut it finely the way you would do onions in a kitchen and added it to my crucible in the hope of reducing the oxide to amorphous elemental boron on further heating. Partington mentions that this can take several hours, even with gas burners…so, as I said just now, it was plain boring.

At some point it must have occurred to me that this was absolutely the ideal time to relieve my boredom by trying something interesting…like the bromine experiment…after all, it was all there…I had access to everything. I went to the adjoining storeroom where the chemicals were kept and they had plenty of potassium bromide and potassium permanganate and in any case, jars of concentrated sulphuric acid were available on each of the working tables.

So, I set up a flat bottom flask with potassium bromide and potassium permanganate (in proportion to their molecular weights as customary). This was corked by a two holed rubber stopper – one hole for the thistle funnel and another for the glass tubing leading to the retort that had been immersed in water to collect the emergent bromine.

I had now to decide between dilute and concentrated sulphuric acid solutions to pour through the thistle funnel. My earlier faulty reasoning, that had led me to conclude that this would be a slow rather than a vigorous reaction, pushed me into choosing the concentrated acid (once again chess-wise you would mark this:??)

All that follows probably took a minute or less, but it was, for sure, the longest minute that I have ever experienced:

I removed the stopper from the bottle of concentrated sulphuric acid, and, anticipating nothing more than the gentlest fizz, I poured a dollop into the thistle funnel. The reaction was immediate. The contents of the flask began to fizz violently and turn into a colour somewhere between strawberry jam and cranberry sauce. More alarming though was the rapid regurgitation of the stuff in the flask back into the thistle funnel. Stuff as in solids liquids and a little gas. Rapid as in faster than one could think. So, don’t think! Remove the stopper and all associated tubing and the retort and place it in the sink under running water. Do it, do it quickly…. Done! But what to do with this miniature Macbethian witches’ brew belching away ominously in the flat bottom flask. Dilute it right? Don’t think…do it quickly! At the back of my mind I was instinctively certain that most of the liquid in the flask was concentrated sulphuric acid and that adding water to it was going to heat it up as the dilution of concentrated sulphuric acid is always accompanied by a significant amount of heat. Why I did not act accordingly was having wrong boiling point of bromine in my head.

To put it plainly in layman’s terms, the reaction had already resulted in a significant quantity bromine, some of it was visibly gaseous but most of it was present as a liquid coexisting uncomfortably, no doubt, with the acid … waiting as it were, to be let out of its prison as a gas, given the pretext! All of this is of course was in retrospect.

So, since the outward or, rather, the visible signs of gaseous bromine were no more than what I had expected, I surmised that adding water would at least put paid to the more ominous aspects of the bubbling mix. So, as they write blandly in chemistry journals: Water was added to the mixture. The result was both unexpected and it was truly spectacular. The heat caused by the dilution of the sulphuric acid was more than enough to free the bromine from the its liquid state. Billows of reddish brown bromine gas spilled out of the flask as if from a smokestack and it took just a few seconds for this to spread throughout the lab. Fresh air…fresh air is what we need I thought. Taking a deep breath, I ran with the flask past the last table, through the open door to the chemistry classroom and finally out from there to the edge of the senior school plateau overlooking the junior school campus.

I must have looked ridiculous to anyone looking: Here’s the mad nerd with a chemical glass thingumajig spewing devilish vapours. But there was almost no one around. All my peers were at their cricket or football (probably football because it was the rainy season game) and the only humans in sight were a couple of juniors (probably excused from games on account of injury or recent illness) down below who were observing me from a distance of about a hundred feet with undisguised interest. I shouted at them to buzz off and they quickly scattered and vanished out of sight as they headed to their dorms. This action of theirs had absolutely nothing whatsoever to do with my having either a commanding personality or being a bully…it was a simple matter of public school etiquette…if a senior asks you to hoof it, then you better hoof it…or else!

That’s when I noticed the drain next to the 67 steps. In retrospect I must say that I must have seen it before hundreds of times but the fact of it had never registered. In fact, if at all I were to ask any of my classmates today whether they recalled a storm drain next to the 67 steps while at school, they would all be pretty blank. Amazing it is how emergencies concentrate the mind. I had a problem and this storm drain was a possible solution. Without thinking too much about it I poured the contents of the flask into the storm drain that sloped steeply downwards. It was a childish reflex reaction of “out of sight, out of mind”. I thought now that “it had all been taken care off”. This was not the case. About half a minute later I saw at the lower end of the drain a tiny cloud of the reddish brown gas mushrooming slowly but surely. At its maximal extent it must have been at least twenty feet high, possibly more. I was transfixed. There was no one but me around. And of course this large stationary cloud of bromine gas. For a little while we stared at each other. Then, quite suddenly there was a gentle gust of wind and the mushroom shaped cloud gradually disappeared. It was as though the genie was saying, “You called me, O Master, so I came, but now, since you don’t have a god-dammed clue what to do with me, I’m outta here!”

Aftermath: As an immediate aftermath, I would like to be able to confess up to some kind of Abraham Lincoln moment, but that could not and did not happen. It could not because the only person to whom I could recount the relevant events in the lab was the chemistry teacher. He would have a choice: Report it upward so that the Headmaster could decide whether a public caning was in order, or, he could report it downward to the head-boy and his prefects who could be counted upon to be almost as rough. Besides, my father was far away preparing for a war that everyone knew was going to come (it came in December 1971) and I was pretty sure that I didn’t want him rushing back on my account. I decided to stay silent. In point of fact, I quietly re-entered the lab, put on the exhaust fans for a bit and then proceeded with my boron trioxide experiment (and finally called it a day at about 5:30 that evening.

For, the record, I did get the scholarship and continued along the natural sciences path till I got an MPhil in Pure Mathematics. But that career line didn’t continue for long. I quit my PhD work in Maths and started doing other things. How I ended up as a professor of music at a film school in my mid-thirties is a subject that may or not form a subject of another blog.