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It turns out that they generally form complex aggregates with two, four, six, or more molecules bonded together, often with solvent molecules. Initiation can be accomplished aldeidoa adding a small amount of iodine or 1,2-diiodoethane, or by using ultra- sound to dislodge the oxide layer.

Here is one example of each, but you will have to wait until Chapter 12 for the details and the mechanisms of the reactions.

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

But at this stage we just want you to appreciate that even the relatively simple chemistry in this chapter is useful in synthesis, in commerce, and in medicine. Reaction of triphenylphosphine with a primary or secondary alkyl halide produces a phosphonium salt The phosphonium salt is deprotonated by a strong base to form the ylide. The details of this sort of chemistry will come in Chapter 14 when you will meet imines as intermediates.

But there is a problem! Aldehydes and ketones react with primary amines and ammonia to yield imines They react with secondary amines to yield enamines. Note that one cyanohydrin was made by the simplest method—just NaCN and acid—while the other came from the bisulfite route we have just discussed.

Aldehydes and ketones react with phosphorous ylides to produce alkenes An ylide is a neutral molecule with adjacent positive and negative charges. 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: Overall it involves an insertion of magnesium into the new carbon—halogen bond.


The second reason that bisulfite compounds are useful is that they are soluble in water. Thioacetals can be converted to CH2 groups by hydrogenation using a catalyst such as Raney nickel.

An excess of water in the presence of an acid catalyst will hydrolyze an acetal to the corresponding aldehyde or ketone.

Aldeídos e cetonas

In parts of Africa the staple food is cassava. An aldehyde or ketone dissolved in an alcohol will form an equilibrium mixture containing the corresponding hemiacetal. The solution is to make a bisulfite compound from it. In this book we shall not be concerned with these details, and it will suffice always to represent organometallic compounds as simple monomeric structures.

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. Making organometallics How to make Grignard reagents Grignard reagents are made by reacting magnesium turnings with alkyl halides in ether solvents to form solutions of alkylmagnesium halide.

This does not usually matter to most chemists as we often want to carry out reactions in organic solvents rather than water. Bisulfite addition compounds Other compounds from cyanohydrins Cyanohydrins can be converted by simple reactions into hydroxyacids or amino alcohols. The reaction is therefore known as an oxidative insertion or oxidative addition, and is a general process for many metals such as Mg, Li which cetomas meet shortlyCu, and Zn.

Now the compound will dissolve in water and release dapsone inside the patient. The table lists some of the most important commercially fetonas organolithiums and Grignard reagents.

Dapsone is insoluble in water. Acylic hemiacetals are generally not stable, however, cyclic five-and sixmembered ring hemiacetals are. Enviado por Karine flag Denunciar. You may ask how this is possible since dap- sone has no aldehyde or ketone—just two amino groups and a cetnoas.


Reactividade de aldeídos e cetonas

Organometallics as bases Organometallics need to be kept absolutely free of moisture—even moisture in the air will destroy them.

Here are some examples.

The trick is to use the formaldehyde bisulfite compound and exchange the OH group for one of the amino groups in dap- sone. The tetrahedral carbon resulting from addition to an aldehyde is less sterically hindered than the tetrahedral carbon resulting from addition to a ketone.

The equilibrum favors a ketone over its hydrate because the tetrahedral ketone hydrate is sterically crowded. But it can matter to medicinal chemists, who make compounds that need to be com- patible with biological systems. Mild acid facilitates departure of the hydroxyl group from the aminoalcohol intermediate without also protonating the nitrogen of the amine starting co mpound.

Some diseases found in eastern Nigeria can be traced to long-term consumption of HCN.

Some people like eating these, but it is unwise to eat too many at one sitting! The glucoside is not poisonous in itself, but enzymes in f human gut break it down and release HCN.

Aldehyde carbonyl groups are more electron deficient because they have only one electron-donating group attached to the carbonyl carbon. Earlier in this chapter we mentioned the difficulty of working with formaldehyde because it is either an aqueous solution or a dry polymer. Xldeidos bisulfite compound of formaldehyde CH2O has special significance. There is also a change in oxidation state of the magnesium, from Mg 0 to Mg II.

The hydrate is also called a gem-diol gem i.