Creative Chemistry: Descriptive of Recent Achievements in the Chemical Industries. Edwin E. Slosson
Now the search for the constitution of benzene is one of the most exciting chapters in chemistry; also one of the most intricate chapters, but, in spite of that, I believe I can make the main point of it clear even to those who have never studied chemistry—provided they retain their childish liking for puzzles. It is really much like putting together the old six-block Chinese puzzle. The chemist can work better if he has a picture of what he is working with. Now his unit is the molecule, which is too small even to analyze with the microscope, no matter how high powered. So he makes up a sort of diagram of the molecule, and since he knows the number of atoms and that they are somehow attached to one another, he represents each atom by the first letter of its name and the points of attachment or bonds by straight lines connecting the atoms of the different elements. Now it is one of the rules of the game that all the bonds must be connected or hooked up with atoms at both ends, that there shall be no free hands reaching out into empty space. Carbon, for instance, has four bonds and hydrogen only one. They unite, therefore, in the proportion of one atom of carbon to four of hydrogen, or CH4, which is methane or marsh gas and obviously the simplest of the hydrocarbons. But we have more complex hydrocarbons such as C6H14, known as hexane. Now if you try to draw the diagrams or structural formulas of these two compounds you will easily get
H H H H H H H
| | | | | | |
H-C-H H-C-C-C-C-C-C-H
| | | | | | |
H H H H H H H
methane hexane
Each carbon atom, you see, has its four hands outstretched and duly grasped by one-handed hydrogen atoms or by neighboring carbon atoms in the chain. We can have such chains as long as you please, thirty or more in a chain; they are all contained in kerosene and paraffin.
So far the chemist found it east to construct diagrams that would satisfy his sense of the fitness of things, but when he found that benzene had the compostion C6H6 he was puzzled. If you try to draw the picture of C6H6 you will get something like this:
| | | | | |
-C-C-C-C-C-C-
| | | | | |
H H H H H H
which is an absurdity because more than half of the carbon hands are waving wildly around asking to be held by something. Benzene, C6H6, evidently is like hexane, C6H14, in having a chain of six carbon atoms, but it has dropped its H's like an Englishman. Eight of the H's are missing.
Now one of the men who was worried over this benzene puzzle was the German chemist, Kekulé. One evening after working over the problem all day he was sitting by the fire trying to rest, but he could not throw it off his mind. The carbon and the hydrogen atoms danced like imps on the carpet and as he watched them through his half-closed eyes he suddenly saw that the chain of six carbon atoms had joined at the ends and formed a ring while the six hydrogen atoms were holding on to the outside hands, in this fashion:
H
|
C
/ \\
H-C C-H
|| |
H-C C-H
\ //
C
|
H
Professor Kekulé saw at once that the demons of his subconscious self had furnished him with a clue to the labyrinth, and so it proved. We need not suppose that the benzene molecule if we could see it would look anything like this diagram of it, but the theory works and that is all the scientist asks of any theory. By its use thousands of new compounds have been constructed which have proved of inestimable value to man. The modern chemist is not a discoverer, he is an inventor. He sits down at his desk and draws a "Kekulé ring" or rather hexagon. Then he rubs out an H and hooks a nitro group (NO2) on to the carbon in place of it; next he rubs out the O2 of the nitro group and puts in H2; then he hitches on such other elements, or carbon chains and rings as he likes. He works like an architect designing a house and when he gets a picture of the proposed compounds to suit him he goes into the laboratory to make it. First he takes down the bottle of benzene and boils up some of this with nitric acid and sulfuric acid. This he puts in the nitro group and makes nitro-benzene, C6H5NO2. He treats this with hydrogen, which displaces the oxygen and gives C6H5NH2 or aniline, which is the basis of so many of these compounds that they are all commonly called "the aniline dyes." But aniline itself is not a dye. It is a colorless or brownish oil.
It is not necessary to follow our chemist any farther now that we have seen how he works, but before we pass on we will just look at one of his products, not one of the most complicated but still complicated enough.
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