Keton

Dari Wikipedia bahasa Melayu

Satu keton adalah samada kumpulan berfungsi dicirikan dengan kumpulan karbonil yang terikat dengan dua atom karbon atau satusebatian kimia yang mengandungi kumpulan berfunsi ini. Satu keton boleh ditunjukkan secara amnya dengan formula di bawah:

R₁(CO)R₂.

Jadual isi kandungan 1 Nomenclature 2 Ciri-ciri Fizikal 3 Ciri-ciri Spektroscopik 4 Sintesis 5 Tindakbalas 6 Keton dalam biologi 7 Penggunaan 8 Lihat juga 9 Rujukan

[Sunting] Nomenclature

In general, ketones are named using IUPAC nomenclature by changing the suffix -e of the parent alkane to -one. For common ketones, some traditional names such as acetone and benzophenone predominate, and these are considered retained IUPAC names Templat:Ref, although some introductory chemistry texts use names such as 2-propanone or propanone.

[Sunting] Ciri-ciri Fizikal

A carbonyl group is polar. This makes ketones polar compounds. The carbonyl groups interact with water by hydrogen bonding. It is a hydrogen-bond acceptor, but not a hydrogen-bond donator, and cannot hydrogen-bond to itself. This makes ketones more volatile than alcohols and carboxylic acids of similar molecular weight.

[Sunting] Ciri-ciri Spektroscopik

Spectroscopy is an important means for identifying ketones. Ketones and aldehydes will display a significant peak in infrared spectroscopy, at around 1700 cm⁻¹ (slightly higher or lower, depending on the chemical environment)

[Sunting] Sintesis

• Ketones can be created by oxidation of secondary alcohols. The process requires a strong oxidising agent such as potassium dichromate or other agents containing Cr(VI). The alcohol is oxidised by heating under reflux in acidified solution. For example propan-2-ol is oxidised to propanone (acetone):

H₃C-CH(OH)-CH₃ → H₃C-CO-CH₃

Two atoms of hydrogen are removed, leaving a single oxygen atom double-bonded to a carbon atom.

• Ketones are also prepared by Gem halide hydrolysis.
• Aromatic ketones can be prepared in the Friedel-Crafts reaction and the Fries rearrangement.

[Sunting] Tindakbalas

ketones engage in many organic reactions:

• Nucleophilic addition. The reaction of a ketone with a nucleophile gives a tetrahedral carbonyl addition compound.
  • the reaction with the anion of a terminal alkyne gives a hydroxyalkyne
  • the reaction with ammonia or a primary amine gives an imine + water
  • the reaction with secondary amine gives an enamine + water
  • the reaction with a Grignard reagent gives a magnesium alkoxide and after aqueous workup a tertiary alcohol
  • the reaction with an organolithium reagent also gives a tertiary alcohol
  • the reaction with an alcohol, an acid or base gives a hemiacetal + water and further reaction with an alcohol gives the acetal + water. This is a carbonyl-protecting reaction.

• Electrophilic addition, reaction with an electrophile gives a resonance stabilized cation.
• the reaction with phosphonium ylides in the Wittig reaction gives alkenes
• reaction with water gives geminal diols
• reaction with thiols gives a thioacetal
• reaction with hydrazine or derivatives of hydrazine gives hydrazones
• reaction with a metal hydride gives a metal alkoxide salt and then with water an alcohol
• reaction of an enol with halogens to α-haloketone
• A reaction at an α-carbon is the reaction of a ketone with heavy water to give a deuterated ketone-d.

[Sunting] Keton dalam biologi

Acetone, acetoacetate and beta-hydroxybutyrate are ketones (or ketone bodies) generated from carbohydrates, fatty acids and amino acids in humans and most vertebrates. Ketones are elevated in blood after fasting including a night of sleep, and in both blood and urine in starvation, hypoglycemia due to causes other than hyperinsulinism, various inborn errors of metabolism, and ketoacidosis (usually due to diabetes mellitus). Although ketoacidosis is characteristic of decompensated or untreated type 1 diabetes, ketosis or even ketoacidosis can occur in type 2 diabetes in some circumstances as well. Acetoacetate and beta-hydroxybutyrate are an important fuel for many tissues, especially during fasting and starvation. The brain, in particular, relies heavily on ketone bodies as a substrate for lipid synthesis and for energy during times of reduced food intake. At the NIH, Dr. Richard Veech refers to ketones as "magic" and increase metobolic efficiency, decreases free radical production and ketone bodies may treat neurological diseases such as Alzheimer's and Parkinson's disease. The heart and brain operate 25% more efficiently using ketones as a source of energy.

[Sunting] Penggunaan

Ketones are often used in perfumes and paints to stabilize the other ingredients so that they don't degrade as quickly over time. Other uses are as solvents and intermediates in chemical industry. Examples of ketons are Acetophenone, Butanone (methyl ethyl ketone) and Propanone (acetone).

[Sunting] Lihat juga

• List of publications in organic chemistry
• Ketosis

[Sunting] Rujukan

1. Templat:Note List of retained IUPAC names retained IUPAC names Link