Oxo compounds

Aldehydes, ketones

IX. Aldehydes

Oxo group ( C=O) at the end of the carbon chain

Homologous series of the aldehydes:

1. Methanal or formaldehyde2. Ethanal or acetaldehyde3. Propanal or propionaldehyde

Nomenclature: In the IUPAC system, the name of the alkane chain loses the terminal "e" and adds „al",

The name, aldehyde, shows how we can prepare them : alcohol dehydrogenization

IX. Aldehydes

Preparation of aldehydes:

Primary alcohol aldehyde

Carboxylic acid aldehyde

oxidation

reduction

Other reactions of aldehydes:

Tollens’ test: Ag+ is reduced to silver metal, which in a clean glass reaction vessel forms a "silver mirror". This feature is used as a test for aldehydes, which are oxidized to carboxylic acids.

R-CHO + 2AgOH R-COOH + 2Ag + H2O

Tollens' reagent can be used to test whether the compound is a ketone or an aldehyde. When adding the aldehyde or ketone to Tollens' reagent, put test tube in a warm water bath.If the reactant under test is an aldehyde, Tollens' test results in a silver mirror. If there is no reaction then the organic substance is a ketone, as they can cannot be oxidized, due to the position of the O atom.

Other reactions of aldehydes:

Tollens’ test:

R-CHO + 2AgOH R-COOH + 2Ag + H2O

IX. Aldehydes

Fehling test:

R-CHO + 2 Cu(OH)2 R-COOH + Cu2O + 2 H2O

It is used as a test for the presence of reducing sugars such as glucose, fructose and maltose, or more generally for the presence of aldehydes Cu2O is red and not soluble in water – red precipitate

Other reactions of aldehydes:

IX. Aldehydes

IX. Aldehydes

In the aldehydes there is no H atom which could make H-bonds. Between the aldehyde molecules there are dipole-dipole interactions

Non polar compoundsAldehydes are soluble in water but this solubility is limited :Only diluted solutions can be made from formaldehyde and acetaldehyde

Physical properties:

Chemical properties:

Chemically the most reactive functional group!!!! C=O

IX. Aldehydes

1. Formaldehyde ( methanal)

-Formaldehyde readily results from the incomplete combustion of carbon-containing materials. -It may be found in the smoke from forest fires, in automobile exhaust, and in tobacco smoke.

-Although formaldehyde is a gas at room temperature, it is readily soluble in water. - It is most commonly sold as a 37% aqueous solution which is called formalin or formol. - An aqueous solution of formaldehyde can be used as a disinfectant as it kills most bacteria and fungi (including their spores). - It is also used as a preservative in vaccinations. - Formaldehyde preserves or fixes tissue or cells by irreversibly cross-linking primary amine groups in proteins with other nearby nitrogen atoms in protein or DNA through a -CH2- linkage.

2. Acetaldehyde ( ethanal):

IX. Aldehydes

-It is a flammable liquid with a fruity smell.

- occurs naturally in ripe fruit, coffee, and fresh bread and is produced by plants as part of their normal metabolism.

- is the chemical that causes "hangovers".

- In the liver, the enzyme alcohol dehydrogenase converts ethanol into acetaldehyde, which is then further converted into harmless acetic acid by acetaldehyde dehydrogenase.

- Acetaldehyde is more toxic than ethanol and is responsible for many symptoms of hangover- Most people of East Asian descent have a mutation in their alcohol dehydrogenase gene that makes this enzyme unusually effective at converting ethanol to acetaldehyde- and about half of such people also have a form of acetaldehyde dehydrogenase which is less effective at converting acetaldehyde to acetic acid. This combination causes them to suffer from the alcohol flush reaction, in which acetaldehyde accumulates after drinking, leading to severe and immediate hangover symptoms. These people are therefore less likely to become alcoholics. - The drug Antabuse also prevents the oxidation of acetaldehyde to acetic acid, with the same unpleasant effects for drinkers. It has been used in the treatment of alcoholism.

IX. Aldehydes

X. Ketones R-CO-R’

Nomenclature: In the IUPAC system, the name of the alkane chain loses the terminal "e" and adds „on",

Oxo group ( C=O) in the middle of the carbon chain

Homologous series of the ketones: (starts from C3)

1. Propanon or aceton2. Butanon3. pentanon

X. Ketones

Preparation of ketones:

Secondary alcohol ketonoxidation

Physical properties of ketones:

Non polar compounds but the ketones with small carbon number are soluble in water e.g. acetonBut with bigger carbon number they are immiscible in water

Chemical properties:

Chemically very reactive compounds

X. Ketones

Keto-enol tautomerism (see before)

2333 CHCCHCHCOCH

OH

- Aceton is an irritant and inhalation may lead to hepatotoxic effects (causing liver damage). - it can cause permanent eye damage -ketosis: is a stage in metabolism occurring when the liver converts fat into fatty acids and ketone bodies (acetone, acetoacetic acid, and beta-hydroxybutyric acid) which can be used by the body for energy. -Ketoacidosis: which is severe ketosis causing the pH of the blood to drop below 7.2. -Ketoacidosis is a medical condition usually caused by diabetes and accompanied by dehydration, hyperglycemia, ketonuria and increased levels of glucagon. -The high glucagon, low insulin serum levels signals the body to produce more glucose via gluconeogenesis, glycogenolysis and ketogenesis. High levels of glucose causes the failure of tubular reabsorption in the kidneys, causing water to leak into the tubules in a process called osmotic diuresis, causing dehydration and further exacerbating the acidosis.

1. AcetonX. Ketones

XI. Carboxylic acids

Homologous series of monocarboxylic acids (only one carboxylic group containing carboxylic acids):

1. Methanoic acid = formic acid2. Ethanoic acid = acetic acid3. Propanoic acid = propionic acid4. Butanoic acid 5. Pentanoic acid

Nomenclature: In the IUPAC system, the name of the alkane chain ( including the carbon atom of the carboxylic group too) loses the terminal "e" and adds „oic", plus acid

XI. Carboxylic acids

Dicarboxylic acids : 2 carboxylic groups containing Carboxylic acids

Long chain monocarboxylic acids are called as fatty acids: e.g. palmitic acid ( hexadecanoic acid) see later

e.g. oxalic acid HOOC-COOH malonic acid HOOC-CH2-COOH maleic acid HOOC-CH2-CH2-COOH

XI. Carboxylic acids

Nameing of carboxylic acids:

CH3-CH2-CH2-CH2-COOH

Distinguishing the carbon atoms in the chain: (IUPAC)

Carbon 1: (first carbon) the carbon which is part of the carboxylic group

α is the first carbon atom after the carbon atom which is included in the Carboxylic group

1.δ γ β α

Prepatration of carboxylic acids:

1. Biological fermentationFormic acidAcetic acid ( vinegar)

2. Synthetic preparation: a. oxidationsAlcohol

carboxylic acidAldehyde

b. Hydrolysis

Ester carboxylic acid + alcohol

XI. Carboxylic acids

oxidation

Hydrolysis +H2O

Physical properties

One of the most polar compounds – strong enough for ionizationMost of them are weak acids

They contain –OH group – they can form H- bondsCarboxylic acids are polar, and form hydrogen bonds with each other or with water – high melting and boiling point

Lower carboxylic acids (1 to 4 carbons) are miscible with water, higher carboxylic acids are very much less soluble due to the increasing hydrophobic nature of the alkyl (carbon) chain. They rather soluble in less polar solvents such as ethers and alcohols.

XI. Carboxylic acids

XI. Carboxylic acids

True solutions: small chain carboxylic acids e.g butanoic acid

Colloid solution : long chain carboxylic acids – they form micells : polar head, non-polar „tail”- the particle size (size of the micells) is 1-1000 nm

XI. Carboxylic acidsChemical properties:

They are weak acids with different Ka

Reactions:

1. Substitution in the carbon chain with halogenforming strong acid (trichloroacetic acid)

2. Substitution in the carboxylic group R-COOHwith halogen forming acyl cloridewith amine group forming acyl amine

Acyl group: R-C=O Acylate or carboxylate : R-C=O O-Formyl

Acetyl…

FormylateAcetylate

XI. Carboxylic acids

3. Dehydratation: removing H2O

Removing water from base or acid we get anhydrate

R-COOH + HOOC-R’ R-C-O-C-R’ + H2O║ ║O O

Acyl anhydrate e.g. acetyl anhydrate

Inorganic anhydrate:

R-COOH + H-O-P=OH-O

H-O

R-C-O-P║ ║O O

OH

OH

+ H2O

-H2O

-H2O

XI. Carboxylic acids

4. Oxidation: decarboxylation

R-COOH R-H + CO2

oxidation

5. Ester formation : alcohol + carboxylic acid (see at alcohols)

In 2 steps : 1. nucleophylic addition 2. water elimination

XI. Carboxylic acids

6. Reaction with amins (-NH2)

a. Acid – base reaction = salt forms

b. Water eliminationacyl amide – peptide bond forms

c. Carboxylic acid + ammonia = acyl amine (H2O elimination) ( substitution of the –OH group)

XI. Carboxylic acids

1. Formic acid ( methanoic acid) HCOOH

From ant – ant acid The principal use of formic acid is as a preservative and antibacterial agent in livestock feed. When sprayed on fresh hay or other silage, it arrests certain decay processes and causes the feed to retain its nutritive value longer, and so it is widely used to preserve winter feed for cattle. In the poultry industry, it is sometimes added to feed to kill salmonella bacteria.

XI. Carboxylic acids

1. Acetic acid (ethanoic acid) CH3COOH

-acetic acid, in the form of vinegar, has been made by bacteria of the genus Acetobacter. Given sufficient oxygen, these bacteria can produce vinegar from a variety of alcoholic foodstuffs. Commonly used feeds include apple cider, wine, and fermented grain, malt, rice, or potato mashes. The overall chemical reaction facilitated by these bacteria is:C2H5OH + O2 → CH3COOH + H2O

The acetyl (acyl) group, derived from acetic acid, is fundamental to the biochemistry.When bound to coenzyme A it is central to the metabolism of carbohydrates and fats.

XI. Carboxylic acidsShort chain saturated monocarboxylic acids

-Formic acid (methanoic acid) : HCOOH, found in insect stings-Acetic acid (ethanoic acid) : CH3COOH component of vinegar -Propionic acid (propanoic acid) : CH3CH2COOH food preservative

Medium chain saturated monocarboxylic acids

-Valeric acid (pentanoic acid) : C4H9COOH

Short chain unsaturated monocarboxylic acids -Acrylic acid (2-propenoic acid) : CH2=CHCOOH, used in

polymer synthesis

Fatty acids medium to long chain saturated and unsaturated monocarboxylic acidsMost commonly occurring saturated fatty acids are:

Butyric acid (butanoic acid) : CH3CH2CH2COOH, found in rancid butter Lauric acid (dodecanoic acid) : CH3(CH2)10COOH, found in coconut oil

Palmitic acid (hexadecanoic acid): CH3(CH2)14COOH Stearic acid (octadecanoic acid): CH3(CH2)16COOH

XI. Carboxylic acids