Ch 114 Combustion of alcohols Alcohols undergo complete combustion to form carbon dioxide and water Denatured alcohol is a useful portable fuel eg for camping stoves as unlike LPG it does not need to be transported in heavy specialized containers It is also used as a solvent ID: 1026241
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1. Alcohols, Carboxylic acid and EstersCh 11.4
2. Combustion of alcohols Alcohols undergo complete combustion to form carbon dioxide and water.Denatured alcohol is a useful portable fuel (e.g. for camping stoves) as, unlike LPG, it does not need to be transported in heavy, specialized containers. It is also used as a solvent.Denatured alcohol is ethanol that has been made toxic and undrinkable by the addition of other chemical additives.A traditional additive was methanol, which formedmethylated spirits (meths): 90% ethanol and 10% methanol. CH3CH2OH + 3O2 2CO2 + 3H2O
3. A chain of carbon atoms can be represented by R when drawing the structure. This is referred to as an R group.Primary, secondary and tertiaryPrimary (1°) alcohols have one R group attached to the carbon to which the OH group is attached.Secondary (2°) alcohols have two R groups attached to the carbon to which the OH group is attached.Tertiary (3°) alcohols have three R groups attached to the carbon to which the OH group is attached.
4. Oxidation of 1° alcohols: aldehydesPrimary alcohols can be oxidized to aldehydes by an oxidizing agent such as an aqueous solution of acidified potassium dichromate(VI).Aldehydes contain a carbonyl group (C=O) at the end of the carbon chain, and are named using the suffix –al.When the symbol equation is written, the oxidizing agent is represented by [O]:RCH2OH + [O] RCHO + H2Opropanal
5. Synthesis of aldehydesWhen aldehydes are prepared by the reaction of a primary alcohol with acidified potassium dichromate(VI), the aldehyde is distilled off and collected, preventing further oxidation.heatwater inwater outmixture of alcohol,dilute sulfuric acid and potassium dichromate(VI)aldehydeice
6. Oxidation of 1° alcohols: carboxylic acidsIf primary alcohols are reacted with an excess of oxidizing agent and refluxed, they can be oxidized to aldehydes and then oxidixed further to carboxylic acids.Carboxylic acids contain a carbonyl group (C=O) at the end of the carbon chain, with a hydroxyl group (OH) attached to the carbonyl carbon.Carboxylic acid are named using the suffix –oic acid.RCH2OH + [O] RCHO + H2ORCHO + [O] RCOOHpropanoic acid
7. Synthesis of carboxylic acids
8. Oxidation of 2° alcohols: ketones Secondary alcohols can be oxidized to ketones by an oxidizing agent such as an aqueous solution of acidified potassium dichromate(VI).Ketones contain a carbonyl group (C=O) attached to any carbon in the chain except a terminal carbon atom, and are named using the suffix –one.propanoneR1CH(OH)R2 + [O] R1COR2 + H2OTertiary alcohols are resistant to oxidation due to the lack of hydrogen atoms on the carbon atom to which the hydroxyl group is attached.
9. Aldehyde, ketone or carboxylic acid?
10. Distinguishing aldehydes and ketones
11. Oxidation of alcohols
12. Reactivity of carboxylic acidsThe reactivity of carboxylic acids results, in part, from the polarization of its bonds.The reactions of carboxylic acids include:neutralisation – the carboxylic acid loses a proton to form a carboxylate saltnucleophilic substitution – the positively-charged carbon is attacked by a nucleophile, resulting in substitution of the OH groupesterification – reaction with an alcohol to form an ester.δ+δ-δ-δ+
13. Forming the carboxylate ionCarboxylic acids are weak acids and partially dissociate in aqueous solution:carboxylate ionThe negative charge is delocalized across the carboxylate group, resulting in a more stable ion. The delocalization is represented by adding a second dotted line to the carbon oxygen bonds, which are both equivalent.
14. Reactions with carbonatesCarboxylic acids are the only organic compounds that are strong enough acids to react with either sodium carbonate or sodium hydrogencarbonate.Reaction of ethanoic acid and sodium carbonate:2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2Osodium ethanoateReaction of methanoic acid and sodium hydrogencarbonate:HCOOH + NaHCO3 → HCOONa + CO2 + H2Osodium methanoateThe formation of bubbles of carbon dioxide gas makes these reactions useful as a test for carboxylic acids.
15. Reactions with alkalisCarboxylic acids will react with alkalis, such as sodium hydroxide, in a neutralization reaction:RCOOH + NaOH → RCOONa + H2OReaction of propanoic acid and sodium hydroxide:Reaction of butanoic acid and potassium hydroxide:CH3CH2COOH + NaOH → CH3CH2COONa + H2Osodium propanoateCH3CH2CH2COOH + KOH → CH3CH2CH2COOK + H2Opotassium butanoate
16. Carboxylic acids forming amidesPrimary amides can be made by reacting a carboxylic acid with ammonia via a condensation reaction producing the amide and a molecule of waterSecondary amides can be formed from a carboxylic acid and an amine via a condensation reaction producing the secondary amide and a molecule of water
17. Esterification Esterification involves refluxing a carboxylic acid and an alcohol with a concentrated sulfuric acid catalyst.The names of esters have two parts: the first is an alkyl group (from the alcohol) and the second is a carboxylate group (from the carboxylic acid).fromalcoholfromcarboxylic acidFor example, methanol and ethanoic acid react to form methyl ethanoate.R1COOH + R2OH R1COOR2 + H2O
18. Esterification
19. Naming estersThe names of esters are based on the carboxylic acid and alcohol from which they are produced. methylethanoateethylmethanoatepropylethanoateThe first component of this ester name, the methyl, is derivedfrom the alcohol methanol. ethanol + methanoic acidpropanol + ethanoic acidThe second component of the name, the ethanoate, is derived from the carboxylic acid ethanoic acid.
20. Naming esters
21. Hydrolysis of esters
22. Esters in fats and oils
23. Naming fatty acidsFatty acids have systematic names as well as common names. For example, the systematic name for oleic acid is octadec-9-enoic acid. Some common fatty acids are explained below.polyunsaturated, found in vegetable oilsCH3(CH2)4(CH═CHCH2)2(CH2)6COOH(octadec-9,12-dienoic acid)linoleicacidmonounsaturated, found in most fats and olive oilCH3(CH2)7CH═CH(CH2)7COOH(octadec-9-enoic acid)oleicacidsaturated, used for making soapsCH3(CH2)14COOH(hexadecanoic acid)palmiticacidsaturated, found in most animal fatsCH3(CH2)16COOH(octadecanoic acid)stearicacidDescriptionFormula and systematic nameCommonname
24. Saturated and unsaturated
25. Making soap and biodiesel
26. Summary of organic synthesis reactions
27. What’s the structure?
28. Multiple-choice quiz