Chapter 12: Organic Chemistry

miscellaneous | dye | perfume | plastic | safety

Miscellaneous

Organic chemistry is the study of carbon compounds, normally with more than one carbon atom, so carbon dioxide, CO₂, is not an organic compound. The term orginally meant compounds from plants and animals because they were too hard for people to make, so they were thought to require an organic origin.

As a carbon chain gets more carbon atoms it's less likely to be a gas. The first four (which are all gases at room temperature) are:

Methane, CH₄
Ethane, C₂H₆
Propane, C₃H₈
Butane, C₄H₁₀

The above gases are called saturated, because they have as many hydrogen atoms as they can. If hydrogen atoms are removed we get other organic compounds known as unsaturated hydrocarbons, such as ethene and ethyne. These are more commonly called ethylene (C₂H₄) and acetylene (C₂H₂). When acetylene burns in air it's and orange colour and very sooty, but when combined with enough oxygen, such as in an oxyacetylene torch, it burns with an extremely hot flame, up to 3,300 °C, and is the hottest burning gas. (Some solids burn hotter.)

Acetylene is the gas used in old caving lamps. Water dripped onto calcium carbide (CaC₂) - normally just called carbide - releasing acetylene gas, which was passed out a nozzle on a caver's headlamp, where it was burned. Carbide isn't used very much any more because dead carbide basically pollutes caves if it is left behind and is a hassle to carry out of the cave.

CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂

Polyunsaturated margarine refers to the hydrogen atoms that have been removed from the carbon chains in the margarine. Poly means many.

Alcohols follow the same naming structure as the above gases, and have one hydrogen atom replaced by hydroxyl (chemical formula OH, like water missing a hydrogen).

Methanol, or methyl alcohol, CH₃OH
Ethanol, or ethyl alcohol, C₂H₅OH

Ethanol is the alcohol in wine, beer, spirits, etc. Both of these can be used as fuels, and in the three years since this page was first published we are now able to buy petrol with 10% ethanol in it. Methanol is used as a fuel in high performance race and drag cars.

Dye

William Henry Perkin thought chemistry was more fun that architecture and convinced his father to let him study chemistry. The rest is history. He attempted something really ambitious (making synthetic quinine) and failed in that, but invented a purple dye known as mauveine or aniline purple. Importantly, he recognised the significance of his find and soon most dyes were synthetically produced. That had a serious effect on the farmers who grew the crops dyes used to be made from.

Chemists quickly went on to produce other dyes, and more recently chemists have used organic dyes to produce dye lasers. Using a dye allows the laser to be tuned to the particular colour wanted.

Wikipedia says Later work on chemical dyes also led to the (accidental) development of modern chemotherapy (see Sulfonamide).

Perfume

After 20 years of making dyes William Henry Perkin was very wealthy and retired from dye making. He returned to chemical research again and made the first synthetic perfume, a naturally occuring chemical named coumarin, which has the scent of newly-mown hay.

Plastic

Leo Baekeland, the inventor of Bakelite, was in a somewhat similar position to William Perkin. Leo Baekeland wasn't the first to discover the substance - he was even warned not to mix the constituent substances because he would wreck his test tubes - but he recognised the significance of the material, and plastics have become a hugely important part of our lives.

Mylar is a trade name for a particular kind of plastic, and is easier to say than "biaxially-oriented polyethylene terephthalate (boPET) polyester film" which is its technical name. Polyethylene terephthalate (PET) is the same sort of plastic that polarfleece and softdrink bottles are made from but boPET film has particular properties. It's a very thin and tough plastic sheet. It's very hard to rip but if torn from an edge will continue to rip, putting up next to no resistance. It can also be coated with aluminium to make it much less permeable to gases, and so is used for helium balloons. Because boPET film is a good dielectric (electrical insulator) it is used in foil capacitors.

Safety

Many organic compounds are necessary for life (such as glucose), but many are also quite toxic.

Methanol can cause blindness and death, and can be absorbed into the blood through the skin. Do not handle pure methanol liquid or inhale methanol vapour, and do not drink any amount of methanol.
Ethanol is toxic in larger quantities. As well as getting people drunk and giving them alcohol poisoning, it can cause birth defects such as foetal alcohol syndrome if consumed by women while they are pregnant. It can affect men's reproductive ability too, with side effects (from binge drinking especially) including genetic damage, resulting in their baby being born with a hare lip or cleft palette.
Teflon™ can cause birth defects. Do not use a frying pan that has been overheated and as a result has a damaged surface. Normally Teflon is fine, since the food being cooked actually prevents the frying pan from overheating.