Christmas chemistry A-Z

Freshen up with BHT and BHA. You are most likely to encounter BHT when you shower on Christmas morning and BHA when you chew some gum later in the day to freshen your breath. These molecules are the preservatives that we rely on to keep things safe because they prevent oxidation of ingredients, which then smell rancid. BHT is butylated hydroxytoluene, also known as E321. While it was once used as a food preservative, it is more likely to be used in personal care products and has been replaced by BHA for food use. BHA is butylated hydroxyanisole, or E320, and is added to edible fats and oils.

Lighten and frighten with flames and bangs. Candles are a traditional part of Christmas and they used to be made from the hard tallow fat of sheep and cows, but they burned with a slightly smoky flame because of unsaturated fatty acids. Candle wax now comes from the petrochemical industry and its saturated long chain hydrocarbons burn with a smokeless flame. The bang from a cracker is the result of a violent reaction between antimony sulfide (Sb₂S₃) and potassium chlorate (KClO₃). When these rub against each other, as you pull the snap in the cracker, they react explosively according to: Sb₂S₃  +  4KClO₃ →  Sb₂(SO₄)₃  +  4KCl.

When we engage in games and other boisterous activities at Christmas parties, we may get rather hot and perspire. Deodorants block the pores in our skin and so deny bacteria the nutrients they feed on. Bacteria are the real culprits responsible for the resulting sweaty odour. A deodorant stick contains aluminium chlorohydrate as its active ingredient. This reacts with moisture to form insoluble aluminium hydroxide and this temporarily puts the pores out of action.

One E-number you might encounter at Christmas is E407, which is an emulsifier used to thicken foods like sauces and ice creams. It is the carbohydrate carrageenan, which is extracted from red seaweed. Another is E621, which is a flavour enhancer added to the gravy you poured over your turkey – see umami flavour below. There are plenty of E-numbers in nibbles and drinks, in sauces and desserts, in treats and sweets, but there may be some misguided individuals in the family who say they want nothing to do with chemicals and for whom E-numbers are seen as a health warning. In fact, an E-number is only allocated to an ingredient that is proved safe, and is awarded by the European Food Safety Authority (EFSA).

It was one of the gifts of the Three Wise Men, and it might be one you’ve received this Christmas if you’ve been given perfume. Frankincense is solidified sap from the Boswellia sacra (olibanum) tree, which grew in the Arabian Peninsula. Its main fragrance ingredient is ß-boswellic acid, which has a citrus/pine smell. Frankincense was used in the time of Ancient Egypt and has been an ingredient in perfumes and ointments ever since, although its main use was in incense as a fragrancer. (The ‘frank’ part of the name means ‘pure’.)

Again this was one of the Wise Men’s gifts and you too might have been given some this Christmas. Today, gold is performing some remarkable feats in the chemical industry in the form of nanogold catalysts. One notable example is in the manufacture of vinyl acetate monomer (VAM), the precursor to the polyvinyls used as adhesives, fibres, and paints, all of which may be around your home. The chemical company Ineos has a plant at Hull, England, which produces 300,000t/year of VAM and it relies on a gold-based catalyst developed by Johnson Matthey. It was Masatake Haruta, of Japan’s Government Industrial Research Institute, who realised gold’s potential more than 25 years ago. He discovered that nanogold would catalyse the conversion of CO to CO₂ at normal temperatures. As such, it is incorporated into safety masks where exposure to CO is a threat.

Holly is a traditional adornment associated with yuletide and probably pre-dates the Christmas festival. With its shiny green leaves and bright red berries, it looks attractive at a time of year when most trees are bare. The berries contain caffeine and theobromine, which is a molecule related to caffeine but with one fewer methyl group. When caffeine is metabolised in the human body, some is converted to theobromine. This chemical is present in small amounts in tea and chocolate, and at various times has been prescribed to treat high blood pressure and as a diuretic. However, eating holly berries will make you vomit all your Christmas goodies because they also contain the alkaloid ilicin.

You will undoubtedly need to settle your stomach at some time over the holiday period. The stomach produces hydrochloric acid (HCl) to aid digestion and sometimes there may be too much for comfort. We can treat indigestion with antacid tablets, indigestion mixtures or acid reflux preventers. Antacids are alkalis and, by their very nature, will do the job. Some are based on calcium carbonate, such as Rennie, and some rely on magnesium hydroxide as in Milk of Magnesia, which has recently had to be reformulated to meet EU regulations. Other remedies are there to prevent acid reflux of which the best known are sodium alginate and Zantac, whose active agent is ranitidine hydrochloride.

Did a loved one buy you a collection of personal care products with which to pamper yourself? If so, then you may have jojoba oil on your skin because this oil is often part of shower gels and hair conditioners, especially if they claim to be made from natural products. You can even buy pure jojoba oil for use as a skin moisturiser. What is unusual about this oil is the composition of its fatty acids, in particular 13,16-docos-dienoic acid, which has 22 carbons with double bonds as indicated, and 11-eisocensnoic, which has 20 carbons with one double bond. Each of these fatty acids accounts for a third of the oil. Whether they provide something extra that other oils lack is a matter of debate, but you can enjoy them all the same.

You might have adorned your Christmas tree with a strip of krypton lights. Krypton has several sharp emission lines in its spectrum, unlike its neighbour neon, which shines predominantly red. Krypton light is whitish and penetrating, which is why it is used in flash photography and for outdoor lights such as hand-held and helmet torches, bike lights and airport runway lights. The home planet of Superman is named after this element – or is it the other way round?

Even on Christmas Day, you will no doubt use something that relies on a rechargeable lithium battery. These kinds of batteries have a high energy output and only lose charge slowly when the device is not in use. In these batteries, lithium ions move from one electrode to the other, and back again when the battery is re-charged. Lithium-air batteries, aka Li-O-2, are currently under investigation and these will even be able to deliver enough current to power your car. They are based on the reversible reaction 2Li + O2 ↔ Li2O2 with air supplying the oxygen.

Kissing under the mistletoe dates back to pagan times, but the berries are poisonous although previous generations used mistletoe juice from to relieve strains, sores, dandruff, warts, and ringworm while an infusion of the berries was drunk as a medicine for epilepsy, colds, fevers, syphilis, gout and worms. The toxic ingredient in the berries is mistletoe lectin and this consists of two large proteins, one of which can attach itself to a cell’s wall, while the other enters the cell and disrupts the production of proteins.

The ones you might encounter at Christmas are N₂O, and even NO, if you play your cards right. Nitrous oxide (N₂O) can affect the brain and give you a mild high, and in the 1800s it was used for this purpose and known as laughing gas. Currently there is a street craze for it, which you inhale from a balloon filled with it. (N₂O is still used as an anaesthetic.) At Christmas it may be present in the cream that you squirt on to your Christmas pudding and it has the approval code E942. However, it is unlikely to set you off laughing. Nitric oxide (NO) can give you a different kind of high. It can dramatically affect bodily functions and is produced by the enzyme NO synthase. It can increase the flow of blood, and is the way to control angina, which happens when the flow of blood to the heart is restricted. NO can also produce an erection by relaxing the muscle that controls the flow of blood into the penis.

These occur naturally in some foods because they are components of plants such as leeks, onions, asparagus and that essential component of Christmas dinner: brussels sprouts. There are three main kinds of oligosaccharides: fructo-oligosaccharides, which consist of short chains of fructose molecules; galacto-oligosaccharides, which are galactose chains; and raffinose, which is a trisaccharide of galactose, glucose and fructose. Fortunately for the microbes that populate our gut, we cannot digest these kinds of foods because we lack the necessary enzyme, whereas they can. When they get to work on brussels sprouts then you need to have some air freshener spray to hand!

More perfume is bought at Christmas than at any other time of year; and it’s not just for women. More and more women are buying perfumes for their menfolk, with names like Brut, Man, Ferrari, Polo, Bang and BlackXS. Perfumes are composed of top notes, which are the most volatile; middle notes, which are often floral; and base notes, which can be quite animalistic. A good perfumer will find a blend that ensures they all evaporate together. Most fragrance chemicals are synthetic and this began in the early years of the last century and became acceptable with the launch of Chanel No.5, still a best-selling perfume. That included the chemical 2-methylundecanal, which offered a purer note, described as conifer. This chemical does occur naturally in kukmquat oil, but only in tiny amounts.

Quince jelly can be quite solid, and used to be eaten as an accompaniment to the traditional meat dishes of poultry and pork that are associated with Christmas. Quince contains chlorogenic acid, of which there are three isomers. You can delight your friends and family by explaining what this is: quinic acid is tetrahydroxycyclohexanecarboxylic acid and if a dihydoroxyphenylpropene goup is attached to one of its three OH groups then is becomes chlorogenic acid – nothing to do with chlorine. They will be astonished at your intellectual ability to remember such impressive words when you’ve had a few drinks.

Red is the colour most associated with Christmas, as in Rudolf’s nose and Santa’s clothes. And, if you want to toast your guests at Christmas, then red wine is a suitable accompaniment to roast turkey. You can even justify a second bottle, because red wines contain the natural phenol resveratrol (3,5,4’-trihydroxystilbene), which provides the colour of red grapes, and hence the wine. Some have seen this chemical as a healthy drink linking it to longevity, and its advantages are explained in terms of its boasting a manganese-containing enzyme, which eliminates superoxide (O₂¯). The diseases that are claimed to benefit from red wine include heart disease, cancer, Huntington’s, Alzheimer’s – and it boosts testosterone. Or so they say.

A white Christmas is something we long to see but rarely do in the UK. But at least we can spray artificial snow around our windows and on the Christmas tree. This consists of a mixture of finely powdered calcium carbonate (CaCO₃) whose particles are coated with sorbitan tristearate wax. Sorbitol is a sugar alcohol and stearic acid is the C18 saturated fatty acid. Sorbitan tristearate keeps the particles of CaCO₃ dispersed in the can and also makes the ‘snow’ stick to the surface it is sprayed on. The propellant that ejects the ‘snow’ is a mixture of propane and isobutane gas.

Titanium dioxide is a brilliant white colour with remarkable covering power, hence its use in paints, kitchen white goods, toothpastes – and it may even have been part of the white icing of a Christmas cake. Nor need you worry, because it is harmless and is an approved colourant with the food code E171. Tinsel used to be made of metal but never from tin despite its name, which comes from the French word estincele meaning sparkle. Down the centuries, tinsel has been made of tin, lead and aluminium. Today, it is of chemical composition consisting of a polymer like the non-flammable PVC made shiny with a thin metal coating of aluminium.

Umami is one of the five basic taste sensations; the others are salt, sweetness, bitterness and acidity. Umami comes from the Japanese word that describes savoury or meatiness and really only entered the English language this century. Umami is associated with two chemicals: monosodium glutamate (MSG) and inosine monophosphate (IMP). While neither of these chemicals has a particularly strong taste in itself, in association with protein they act as powerful flavour enhancers. The gravy of your Christmas dinner might contain a little Bisto or Kikkoman sauce to enhance its flavour, in which case you will imbibe some MSG (E621). And forget Chinese restaurant syndrome, which MSG was supposed to cause. It turned out to be little more than a media scare.

This flavour molecule may well have been in the custard you poured over your Christmas pudding. Vanilla is produced by orchids of the genus Vanilla and especially the flat leaved variety. The amount extracted from plants is around 100t/year although many products claim that their vanilla flavouring is so sourced. A little might be, but the demand for vanilla worldwide is now around 20,000t/year and most is produced by the chemical industry, because it is a relatively simple molecule and indistinguishable from that produced by nature. If a product says it is made with natural vanilla then it can be so described even if it contains but a trace. To say it is made from natural vanilla requires it to be exclusively so.

This traditional drink of Scottish origin is now made all over the world. Because you are celebrating Christmas, you might treat yourself to a crème de la crème of whisky, which is a single-cask, single-malt, single-distillery whisky. It will have been stored in an old port wine cask for many years to achieve the perfect combination of chemicals that delights the palate. You might even reward yourself with a special treat: a bottle of Glenfiddich 50-year-old whisky. It costs a mere £15,000. Other brands are of course available and may be slightly cheaper. Sip it gently and enjoy its methanol, isobutanol, 3-methyl-1-butanol, and ethyl acetate, to name but a few of its molecules. And, of course, its all-important ethanol.

Xylitol’s common name is birch sugar, but it is produced commercially by fermentation. Xylitol, 1,2,3,4,5-pentahydroxypentane, is as sweet as sugar but has a third fewer calories. Chewing gum and toothpaste are the main applications for xylitol, and the main benefit is that, unlike sugar, xylitol cannot be broken down by bacterial to release the acids that cause tooth decay. So while everyone else is tucking into the chocolates as they watch the Queen’s speech, you can sit smugly by and chew gum, and ready to explain its chemistry when her speech is finished.

You are likely to have encountered this metal in a gift. Yttrium-aluminium garnet, known as YAG (Y₃Al₅O₁₂) is very hard and makes a sparkling diamond-like gemstone. These were popular as ‘bling’ in the 1990s until they were replaced by cubic zirconia, which was much cheaper. When YAG is doped with cerium it is used in white LED lights. If anyone asks, you might point out that yttrium is one of four elements named after the village in Sweden where it first came to light. The others are ytterbium, terbium and erbium.

This might also been received as a gift in the form of jewellery. Zircon is zirconium silicate (ZrSiO₄) and is a semi-precious gemstone that has been known since ancient times.

When cut and polished, a zircon crystal shines with an unusual brilliance because of its high refractive index and colourless specimens look like diamonds. Cubic zirconia, aka CZ, has the same crystal structure as diamond and even outshines it. Gem quality CZ crystals were first made in Soviet Russia in the early 1970s and commercial production began in 1976 using specially designed furnaces. CZ may not be as hard as diamond but nevertheless it is as hard as other gemstones and it comes at the upper end of the scale of hardness: 8.5 Mohs, compared with diamond’s 10.