By Mark M. Green (sciencefromaway.com)
I’m old enough to remember cars that knocked, especially when too much was asked of the engine, as when accelerating up a hill in too high a gear. In an internal combustion engine, the fuel air mixture in the cylinder is supposed to ignite when the spark plug fires and the fuel air mixture explodes. All explosions produce heat—the temperature in the cylinder increases. In a contained space as within the cylinder the increase in temperature increases the pressure. Hot molecules move around faster (not like us who tend to get sleepy), hence higher pressure. The cylinder has a moveable part called a piston, which responds to the pressure increase by being forced to change its position in the cylinder, to relieve the pressure increase, to give the heated up molecules more room to move about. The piston is connected to something called a crankshaft, which turns as a consequence of the piston’s motion, converting the up down motion of the piston to turning motion, which is transferred to the wheels of the car. Off we go. The timing of the motion of the pistons has to be tightly controlled, which is the job of the timing of the firing of the spark plugs. If the heat increase from the ignition of the fuel air mixture takes place without waiting for the spark, disorder ensues causing knocking, which comes from engine parts moving out of sync with each other. Low octane fuel is responsible for this out of sync ignition. This causes loss of power and knocking can even be severe enough to destroy the engine.
We don’t hear much knocking now because we have better fuel, that is, gasoline with what is called a higher octane rating. Octane rating is assigned based on the ability of the fuel to suppress knocking. This has to do with molecules and what goes on in the petroleum industry. On March 31, 1937, Sun Oil Company, now Sunoco, conducted an experiment at their Marcus-Hook plant near the Delaware River in Pennsylvania. They forced some crude waste oil through a macaroni shaped catalyst at close to 900 degrees and out came over 7,000 barrels of gasoline with an octane rating of 81 compared to the usual gasoline produced at that time with an octane rating of 60, which caused some knocking. If you put 60 octane rating gasoline in your more powerful modern car the knocking could be severe enough to possibly cause destruction of the engine. An octane rating of 81, which greatly improved performance in the cars at that time is getting close to the octane rating in the engines in our modern cars. Regular at the gas station is about 87.
That macaroni shaped catalyst was an important discovery arising from the work of a French immigrant to the United States, Eugene Houdry, an inventor of considerable ability who loved racing cars and was sick of the limit on his speed by inferior gasoline. He did other things too, like inventing the first catalytic converter for cars to reduce exhaust emissions contributing to smog. It’s no trivial matter that Houdry’s higher octane rated fuel is widely credited with giving British warplanes the power to repel the Nazi planes which had to depend on their lower octane fuel, therefore limiting their performance. The Germans were trying to bomb the British into submission during World War II in preparation for the Nazi invasion of the United Kingdom.
The macaroni shaped catalyst, which Houdry discovered was based on certain kinds of clay, which can be composed of the elements silicon, aluminum and oxygen. On treatment with acids this kind of clay causes the molecules in the waste oil to become positively charged. In chemistry we call such molecules carbocations, carbo for carbon and cation for positive. Molecules like to be neutral, not charged and given a charge the molecules try to get rid of the charge. One way to do that is to change how the carbon atoms in the molecule are connected to each other, to change the molecular shape, what chemists called rearrangements. Molecules also try to give the charge away to another molecule, a kind of passing the buck. All these changes led to the 81 octane rating fuel.
No one in those days understood that positively charged molecules are at work in our livers, not petroleum based molecules but biologically compatible molecules. These in vivo molecules, not receiving their positive charges by macaroni shaped clay derived catalysts but rather by enzymes, feel the same desire, as those in the petroleum industry, to pass the buck and change their shape. These changes occur within all of plant and animal life. In us the positively charged molecules lead to the formation of cholesterol, a molecule that undergoes further changes to produce the sex hormones. It’s one of those fascinating aspects of the chemical sciences that what we discover is happening outside of us, can be related to what happens within us. And carbocations are just one example of that truth.
