Lecture 3. Aldehydes and Ketones PDF

Organic Chemistry Faculty of Medicine and Stomatology One-step educational program ,,Medicine” First semester of the program Dr. Nino Qurashvili Aldehydes and Ketones Perfume in Ancient Egypt  Ancient Egyptians associated fragrances with the gods and recognize...

Organic Chemistry Faculty of Medicine and Stomatology One-step educational program ,,Medicine” First semester of the program Dr. Nino Qurashvili Aldehydes and Ketones Perfume in Ancient Egypt  Ancient Egyptians associated fragrances with the gods and recognized their positive effect on health and wellbeing  Perfumes were generally applied as oil-based solution  The first stage in making a perfume is the extraction of the fragrant essential oils from plants Aldehydes Aldehydes were discovered at the beginning of the 19th century by a German chemist, Baron Von Liebig, who first isolated these molecules His discoveries have greatly influenced industrial agriculture and modern perfumery "In those days, the only way to create fresh fragrances was to use citrus such as lemon, bergamot and orange. These things are very fresh and very charming, but they don't last on the skin" Aldehydes  It took him several months to perfect a new fragrance but eventually he came up with 10 samples and presented them to Chanel.  They were numbered one to five and 20 to 24. She picked number five. Chanel later said, "It was what I was waiting for. A perfume like nothing else. A woman's perfume, with the scent of a woman." Aldehydes in nature Cinnamaldehyde - cinnamon civetone (a ketone) - is used to provide the musky odor of many perfumes Formaldehyde is a component of many building materials The ketones testosterone and estrone -hormones responsible for our sexual characteristics aldehydes and ketones plays a role in how we digest food Nomenclature of Aldehydes & Ketones Aldehydes contain the carbonyl group bonded to at least one hydrogen atom carbonyl functional group Ketones contain the carbonyl group bonded to two carbon atoms. R - Alkyl group alkyl group is an alkane missing one hydrogen IUPAC system of nomenclature of Aldehydes  al is attached as a suffix to parent alkane for the naming of aldehydes  The aldehyde group is always attached at the end of the main carbon chain, and hence the 1st position in the numbering is always assigned to it  It is not always necessary to include numbering in the naming Naming of Aldehydes 3- methyl 4- brom Pentanal 2 2 methyl-3 heqsanal chloropentan oxo butanal al Butanal Ethanal 3- methylbutanal 4- oxopentanal IUPAC system of nomenclature of Ketones  the suffix –one is assigned for the ketones  The numbering of the chain usually starts from the end such that the carbonyl carbon gets the lowest number 2-Butanone 2-Methyl-3-pentanone 2-Hexanone 3-hexanone Pentan 3-one Physical properties of aldehydes and ketones Smell - Except for the lower carbon aldehydes, which have unpleasant odors, all other aldehydes and ketones generally have a pleasant smell. As the size of the aldehyde and ketone molecule increases, the odor becomes less pungent and more fragrant Solubility - Aldehydes and ketones up to four carbon atoms are miscible with water. This is due to the presence of hydrogen bond association between the polar carbonyl group and water molecules  Solubility of aldehydes and ketones in water decreases rapidly on increasing the length of the alkyl chain (carbon chain)  The higher members with more than four carbon atoms are practically insoluble in water. Physical properties /The boiling point Propane Propanal Propanone Propanol - 42oC 50oC (acetone) 97oC three-carbon Propionaldehyde 56oC Primary alcohol alkane Ketone London dispersion dipole–dipole forces hydrogen bonding with forces (van der Waals water molecules forces) Aldehyde and Ketone (with dipole-dipole attractions as well as dispersion forces) has a boiling point higher than the similarly sized alkane which only has dispersion forces. However, the aldehyde's boiling point isn't as high as the alcohol's. In the alcohol, there is hydrogen bonding as well as the other two kinds of intermolecular attraction Chemical Properties of Aldehydes and Ketones  carbon-oxygen double bond is highly polar  The slightly positive carbon atom in the carbonyl group can be attacked by nucleophiles A nucleophile:  negatively charged ion - a cyanide ion, CN-  slightly negatively charged part of a molecule -lone pair on a nitrogen atom in ammonia, NH3  carbon-oxygen double bond gets broken Oxidation An aldehyde has a hydrogen atom attached to the carbonyl group. This makes the aldehydes very easy to oxidise. Ethanal, CH3CHO, is very easily oxidized to carboxylic acids with the same number of carbon atoms. Tollens’ silver mirror test Silver ion as an oxidant is expensive but has the virtue that it selectively oxidizes aldehydes to carboxylic acids. In the Tollens’ silver mirror test, the silver–ammonia complex ion is reduced by aldehydes (but not by ketones) to metallic silver. We need NH4OH to make Tollens’ reagent, because Ag2O is not soluble in water Tollens’ silver mirror test https://www.youtube.com/watch?v=7I-y3I3VzM8 https://www.youtube.com/watch?v=WMfoLhTYOWU Chemical Properties of Aldehydes and Ketones Ketones can be oxidized, but require special oxidizing conditions Adipic acid or hexanedioic acid is the organic compound with the formula (CH2)4(COOH)2. From an industrial perspective, it is the most important dicarboxylic acid: about 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for the production of nylon. Reactions of Formation of Hydrates Water, like alcohols, is an oxygen nucleophile and can add reversibly to aldehydes and ketones. For example, formaldehyde in aqueous solution exists mainly as its hydrate The hydrates cannot be isolated because they readily lose water to reform the carbonyl compound; equilibrium constant of this reversible reaction is less than 1 Reactions of Formation of Hydrates An exception is trichloroacetaldehyde (chloral), which forms a stable crystalline hydrate, CCl3CH(OH)2 Addition of Alcohols: Formation of hemiacetals Alcohols are oxygen nucleophiles alcohols are weak nucleophiles; an acid catalyst is required. The product is a hemiacetal; it contains both alcohol and ether functional groups on the same carbon atom. The addition is reversible Cyanohydrins Hydrogen cyanide adds reversibly to the carbonyl group of aldehydes and ketones to form cyanohydrin. A basic catalyst is required Apheloria corrugata A brightly colored, toxic millipede (Apheloria corrugata) What makes Apheloria corrugate unique? Apheloria corrugate is a chemistry marvel. It produces hydrogen cyanide (HCN). HCN, also known as cyanide, is a well-known poison that once inhaled will compromise the respiratory processes on a molecular level and in high enough doses result in death Cyanohydrins Acetone reacts as follows Learning Objectives 1. Aldehydes and Ketones in nature 2. Use of Aldehydes and Ketones 3. Nomenclature of Aldehydes & Ketones 4. Main functional group 5. Naming of Aldehydes and ketones according to IUPAC system 6. Physical properties of aldehydes and ketones 7. Chemical Properties of Aldehydes and Ketones 8. Oxidation -Tollens’ silver mirror test 9. Reactions of Formation of Hydrates 10.Formation of hemiacetals 11.Cyanohydrins Thank You