Chapter 23 – Infographic descriptions

23.1a Coronavirus: How hand sanitisers protect against infections

Alcohol-based sanitizers contain 60-95% alcohol. Most contain either ethanol, n-propanol, isopropanol, or combination of these.

Chlorhexidine and benzalkonium chloride are also bound in some sanitizers. Both are also used in non-alcohol-based sanitizers.

Other ingredients include glycerol, which acts as a moisturizer to stop your skin drying out. Hydrogen peroxide is added to prevents bacterial contamination in the hand sanitizer.

Alcohols in hand sanitizers after (denature) the structure of proteins. They destroy the cell wall and membranes of bacteria cells, and the envelope of viruses (including coronavirus). They’re less effective against non-enveloped viruses. Non-alcohol-based sanitizers also kill bacteria but are less effective against viruses.

Hand sanitizers with minimum of 60% alcohol are effective if applied generously. However, they don’t kill all virus types and are less effective on dirty or greasy hands.

Hand washing with soap for 20 seconds washes away bacteria and viruses, and also removes dirt and grease. Antibacterial soaps are no more effective.

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23.2a Food, Cosmetics & Explosives – The Versatility of Glycerol

Also known as glycerin, glycerol is produced as a by-product of soap-making and can also be produced synthetically.

Glycerol (Propane-1,2,3-triol) is colourless, odourless, and viscous liquid. Glycerol: [latex]C_{3}H_{8}O_{3}[/latex].

In the food industry: There are a number of different uses for glycerol in the food industry. It can be used as a sweetener in drinks , as an important moistening agent for baked goods, and is also added to confectionary to prevent sugar crystallization. Additionally, it is often used as a solvent for food colourings, and higher levels can have a preservative effect.

In anti-freeze: Glycerol was historically used as an anti-freeze, since it can form strong hydrogen bonds with water, lowering the freezing point. It was succeeded by ethylene glycol, but as this is toxic to humans, glycerol is being reconsidered as an non-toxic alternative.

In personal care products: Glycerol is used as a method of improving smoothness of toothpaste, skin care products, shaving cream, soaps, and hair-care products. It serves as an emollient and lubricant in these products. It is also found in pharmaceuticals, where it is commonly used as a humectant to stop creams drying out, and as a tablet-holding agent.

As a precursor to explosives: Glycerol can be reacted with a mixture of sulfuric acid and nitric acid to produce nitroglycerin, an explosive liquid commonly used in dynamite and other propellants. This compound is also used as a medication for ischemic heart disease.

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23.4a A Guide to Oxidation Reactions of Alcohols

Compounds containing the alcohol functional group (-OH) can be oxidized to produce carbonyl compounds.

The reagents:

• Primary (1^o) alcohol: Carbon attached to -OH has one other carbon directly attached.
• Secondary (2^o) alcohol: Carbon attached to -OH has two other carbons directly attached.
• Tertiary (3^o) alcohol: Carbon attached to -OH has three other carbons directly attached.

Alcohols can be oxidized to carbonyl compounds (containing a C=O bond) using an oxidizing agent. Acidified dichromate (VI) salts can be used, though due to their toxicity alternative reagents can also be utilized, such as pyridinium chlorochromate (PCC).

• Sodium dichromate: [latex]Na_{2}Cr_{2}O_{7}[/latex]
• Potassium dichromate: [latex]K_{2}Cr_{2}O_{7}[/latex]

The type of compound obtained from the reaction depends on the starting alcohol. When an oxidation reaction is carried out with a dichromate salt, the dichromate ion (Cr₂O₇^2-) is reduced to the Cr³⁺ ion, giving a colour change from orange to dark green.

Products with different alcohols:

• Primary alcohol (orange) distils to Aldehyde (dark green) and refluxes to Carboxylic acid.
• Secondary alcohol (orange) refluxes to Ketone (dark green).
• Tertiary alcohol (orange) distils to no reaction (orange).

The apparatus:

An aldehyde can be obtained from primary alcohols using distillation. Otherwise, heating under reflux is used to make sure the alcohol is fully oxidized before distilling from the product.

• Distillation:  Primary alcohol to aldehyde (excess alcohol used). Elevated flask of alcohol and acidified dichromate heated, water cooling tube is used to condense product and the distilled product collects in another flask.
• Heating under reflux: Primary alcohol results in carboxylic acid (excess oxidization agent used) or secondary alcohol results in ketone.  Heat alcohol and acidified dichromate in a pear-shaped flask, water cooling tube is used to condense the reaction product which drops back into the pear-shaped flask.

Testing for reaction products:

Oxidizing agents can be represented simply in chemical equations as [O].

Ethanol reacts with [O] resulting in Ethanal which reacts with [O] to create Ethanoic acid. Note: In step 1, water (H₂O) is lost as a side product of the reaction.

[latex]3C_{2}H_{5}OH+2Cr_{2}O_{7^{2-}}+16H^{+} \rightarrow 3CH_{3}COOH + 4 Cr^{3+} +11H_{2}O[/latex] Dichromate (orange) to Chromium ion (green)

There are two different chemicals reactions that can be used to identify the products of oxidation reactions.

Fehling’s solution: Contains complexed [latex]Cu^{2+}[/latex] ions. Aldehydes reduce these ions to red copper (I) oxide. Ketones don’t react with Fehling’s solution.

• Aldehyde (warm) reacts changing blue to red.
• Ketone (warm) solution remains blue; no reaction.

Tollen’s reagent: Contains the diamine silver ion, [latex]\sqsubset Ag\left ( NH_{3} \right )_{2}\sqsupset ^{+}[/latex]. Aldehydes reduce this to metallic silver, forming a silver mirror on the glass surface.

• Aldehyde (warm) reacts changing colourless to silver mirror (or grey silver precipitate).
• Ketone (warm) solution remains colourless; no reaction.

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23.4b What causes hangovers? A biochemical mystery

Alcohol in your body: In the liver, the alcohol dehydrogenase enzyme converts ethanol to acetaldehyde. The dehydrogenase enzyme then converts that acetaldehyde into acetate. Acetate is broken down into carbon dioxide and water, then eliminated from the body. On average the liver breaks sown alcohol at the rate of one unit (8 grams of 10 milliliters of pure alcohol) every hour.

1. Dehydration: Alcohol has a diuretic effect: during alcohol intoxication the release of the anti-diuretic hormone (ADH) vasopressin is decreased, increasing urination. Alcohol-induced dehydration has been suggested as a cause for some hangover symptoms, but research suggest it isn’t a major factor.
2. Acetaldehyde: Acetaldehyde is rapidly converted in the into acetate in the liver. It is produced by the breakdown of alcohol and has toxic effects that could cause hangover symptoms. Acetaldehyde concentration doesn’t significantly correlate with hangover severity. Disulfiram is a drug to support treatment of alcoholism and inhibits the breakdown of acetaldehyde producing unpleasant hangover-like symptoms.
3. Congeners: Congeners are compounds other than ethanol in drinks including alcohol such as: methanol which breaks down into toxic formaldehyde and formic acid. Congers can increase hangover severity.
4. Immune systems: Cytokines are small proteins released by cells which affect other cells and play an important role in the immune system. Alcohol causes changes in cytokines concentration in the immune system. Studies have shown the effects caused by some cytokines are very similar to those of a hangover, strongly supporting their roles. IL-12 and IFN-y-concentration changes show significant correlations with hangover severity.

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23.5a Canada Day – The Chemistry of Maple Syrup

Maple syrup is the largest commercially produced product derived from tree sap.

Sucrose is the main sugar in maple syrup, making up almost 70% of its composition.

Maple syrup is slightly acidic due to presence of several organic acids, most abundant is malic acid (around 0.5%).

Phenolic compounds in maple syrup form from degradation of lignin in sap, though some like quebecol form in the syrup-making process. Some contribute to syrup flavour, though exact combination of compounds remains unclear.

Maple syrup is graded according to colour, but the exact compounds behind colouration is unclear. Maillard reactions, caramelization, and formation of polycarbonyl compounds have all been implicated.

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23.6a The Chemistry of Foxgloves – Poison & Medicine

The vibrancy of foxgloves belies their poisonous nature; but the same compounds that make them poisonous can also be used in medicine.

All parts of the foxglove contains compounds called cardiac glycosides, including the structurally similar digoxin and digitoxin. Ingestion of these compounds can cause nausea, vomiting, diarrhoea, and an irregular heart beat. They disable cell sodium-potassium ion pumps, leading to increased cell sodium and calcium ion concentration. This slows the heart rate, which can lead to a heart attack and death.

Though poisonous in large amounts, in small doses digoxin can be used to manage some heart conditions, including abnormal heat rhythms and heart failure. It increases the force of the heart’s contraction and consequently the volume of blood pumped with each contracting beat, and also causes the heartbeat to slow.

1. Increase [latex]Na^{+}[/latex] Sodium ion concentration and [latex]Ca^{+}[/latex] Calcium ion concentration.
2. Results in increase force of contraction in the heart, increased volume of blood per beat, decrease in heart rate.

The therapeutic levels of digoxin don’t differ greatly from those at which toxic effects are seen, and as such dosages must be carefully monitored.

• Therapeutic range: 0.8-2.0 nanograms per militlitre of blood.
• Toxic level: greater than 2.0 nanograms per militlitre of blood.

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23.7a The Chemistry of Body Odours – Sweat, Halitosis, Flatulence & Cheesy Feet

Body odour is the result of bacterial activity producing odourous compounds. Here, we look at some of the main components in particular odours.

Halitosis: (from the mouth)

• Methanethiol; smells like sulfur, garlic
• Hydrogen sulfide; smells like sulfur, rotting eggs
• Dimethyl sulfide; smells like cabbage, sulfur, sweet

Underarm Odour: (from the underarms)

• (E)-3-methyl-2-hexenoic acid; smells like goat
• (S)-3-methyl-3-sulfanylhexan-1-ol; smells like onion
• 3-hydroxy-3-methylhexanoic acid; smells like cumin

Flatulence: (from the digestive system)

• Hydrogen sulfide; smells like sulfur, rotting eggs
• Methanethiol; smells like sulfur, garlic
• Dimethyl sulfide; smells like cabbage, sulfur, sweet

Foot Odour: (from the feet)

• Methanethiol; smells like sulfur, garlic
• Propanoic acid; smells like pungent, rancid, sour
• Isovaleric acid (3-methylbutanoic acid); smells like cheesy, fermented, rancid

Read more about “The Chemistry of Body Odours – Sweat, Halitosis, Flatulence & Cheesy Feet [New tab]” by Andy Brunning / Compound Interest, CC BY-NC-ND

Attribution & References

Compound Interest infographics are created by Andy Brunning and licensed under CC BY-NC-ND

Except where otherwise noted, content on this page has been created as a textual summary of the infographics used within our OER. Please refer to the original website (noted below each description) for further details about the image.