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Veja grátis o arquivo Aldeidos e cetonas (1) enviado para a disciplina de Química Orgânica II Categoria: Outros – Veja grátis o arquivo aldeidos e cetonas enviado para a disciplina de Química Orgânica Categoria: Aulas – Veja grátis o arquivo a aldeídos e cetonas QUI 4 enviado para a disciplina de Química Orgânica II Categoria: Aulas – 4 –

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The ether solvent is essential for Grignard formation because 1 ethers unlike, say, alcohols or dichloromethane will not react with Grignards and, more impor- tantly, 2 only in ethers are Grignard reagents soluble.

The tetrahedral carbon resulting from addition to an aldehyde is less sterically hindered than the tetrahedral carbon resulting from addition to a ketone. The reaction scheme is easy enough to draw, but what is the mechanism?

Acetal formation is reversible An excess of water in the presence of an acid catalyst will hydrolyze an acetal to. Making organometallics How to make Grignard reagents Grignard reagents are made by reacting magnesium turnings with alkyl halides in ether solvents to form s of alkylmagnesium halide. The same arguments hold for the C—Mg bond of Grignard reagents. Aldehydes and ketones react with phosphorous ylides to produce alkenes An ylide is a neutral molecule with adjacent positive and negative charges.

In parts of Africa the staple food is cassava. In Chapter 5 you saw how triethylamine forms a complex with the Lewis acid BF3, and much the same happens when an ether meets a metal ion such as magnesium or lithium: But it can matter to medicinal chemists, who make compounds that aldeiros to be com- patible with biological systems. The second reason that bisulfite compounds are useful is that they are soluble in water. Some small that is, low molecular weight aldehydes and ketones are water-soluble—acetone is an exam- ple.


Iodides, bromides, and chlorides can be used, as can both aryl and alkyl halides, though they cannot contain any functional groups that would react with the Grignard reagent once it is formed.

Acylic hemiacetals are generally not stable, however, cyclic five-and sixmembered ring hemiacetals are. Some diseases found in eastern Nigeria can be traced to long-term consumption of HCN. Formation of the acetal proceeds via the corresponding hemiacetal An acetal has two alkoxyl groups bonded to the same carbon.

Initiation can be accomplished by adding a small amount of iodine or 1,2-diiodoethane, or by using ultra- sound to dislodge the oxide layer. Each inserting reaction requires two atoms of lithium and generates one equivalent of lithium halide salt.

aldeidos e cetonas

Carbon atoms that carry a negative charge, for example Me—, are known as carbanions. Aldehydes and ketone react with HCN to form a cyanohydrin A catalytic amount of cyanide helps to speed aldeios reaction. But at this stage we just want you to appreciate that even the relatively simple chemistry in this chapter is useful in cetohas, in commerce, and in medicine.

Secondary amines cannot form a neutral imine by loss of a second proton on nitrogen An enamine is formed instead.

Aldeídos e cetonas

But there is a problem! The equilibrum favors a ketone over its hydrate because the tetrahedral ketone hydrate is sterically crowded.

Dapsone is insoluble in water. Acetal formation from ketones and simple alcohols is less favorable than formation from aldehydes. Dissolving aldehydes or ketones in water causes formation of an equilibrium between the carbonyl compound and its hydrate.

CAPAldehydes and Ketones I [Modo de Compatibilidade] – aldeidos e cetonas

The true structure of organolithiums and Grignard reagents is rather more complicated! This food contains substantial quantities of the glucoside of acetone cyanohydrin a glucoside is an acetal derived from glucose. Eventually 50 mg HCN per g of alreidos can be released and this is enough to kill a human being after a meal of unfermented cassava. How to make organolithium reagents Organolithium compounds may be made by a similar oxidative insertion reaction from lithium metal and alkyl halides.


Bisulfite addition compounds Other compounds from cyanohydrins Cyanohydrins can be converted by simple reactions into hydroxyacids or amino alcohols.

Here are some examples. Now the compound will dissolve in water and release dapsone inside the patient. Some people like eating these, but it is unwise to eat too many at one sitting!

The driving force for the last reaction is formation of the aldeidis strong phosphorusoxygen double bond in triphenylphosphine oxide.

The mechanism of the reaction is not completely understood but a possible but probably not very accurate way of writing the mechanism is shown here: As with Grignard formation, there is really very little limit on the types of organolithium that can be made this way. The trick is to use the formaldehyde bisulfite compound and exchange the OH group for one of the amino groups in dap- sone.

Aldehydes and ketones react with primary amines and ammonia to yield imines They react with secondary amines to yield enamines. Dapsone is an antileprosy drug.