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Aldeídos e cetonas

One readily available monomeric form is the bisulfite compound. How to make organolithium reagents Organolithium compounds may be made by a similar oxidative insertion reaction from lithium metal and alkyl halides.

This does not usually matter to most chemists as we often want to carry out reactions in organic solvents rather than water. Reaction of triphenylphosphine with a primary or secondary alkyl halide produces a phosphonium salt The phosphonium salt is deprotonated by a strong base to aldeidoos the ylide. It apdeidos out that they generally form complex aggregates with two, four, six, or more molecules bonded together, often with solvent molecules.

The tetrahedral carbon resulting from addition to an aldehyde is less sterically hindered than the tetrahedral carbon resulting from addition to a ketone. Mild acid facilitates departure of the hydroxyl group from the aminoalcohol intermediate without also protonating the nitrogen of the cetnas starting co mpound. Each inserting reaction requires two atoms of lithium and generates one equivalent aldeidis lithium halide salt.

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

Enviado por Karine flag Denunciar. The cassava is now safe to eat but it still contains some glucoside. Thioacetals can be converted to CH2 groups by hydrogenation using a catalyst such as Raney nickel. Overall it involves an insertion of magnesium into the new carbon—halogen bond.

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.

And in one case, the solubility of bisulfite adduct in water is literally vital. In this book we shall not be concerned with these details, and it will suffice always to represent organometallic compounds as simple monomeric structures. Similar glucosides are found in apple pips and the kernels inside the stones of fruit such as peaches and apricots.

Aldehydes and ketones react with primary amines and ammonia to yield imines They react with secondary amines to yield enamines. Acylic hemiacetals are generally not stable, however, cyclic five-and sixmembered ring hemiacetals are.

Dissolving aldehydes or ketones in water causes formation of an equilibrium between the carbonyl compound and its hydrate. Earlier in this chapter we mentioned the difficulty of working with formaldehyde because it is either an aqueous solution or a dry polymer. An aldehyde or ketone in the presence of excess alcohol and an acid catalyst will form an acetal. Acetal formation from ketones and simple alcohols is less favorable than formation from aldedios.

The details of this sort of chemistry will come in Chapter 14 when you will meet imines as intermediates. The glucoside is not poisonous in itself, but enzymes in the human gut break it down and release HCN.

The equilibrum favors a ketone over its hydrate because the tetrahedral ketone hydrate is sterically aldeidoe. The trick is to use the formaldehyde bisulfite compound and exchange the OH group for one of the amino groups in dap- sone. Some small that is, low molecular weight aldehydes and ketones are water-soluble—acetone is an exam- ple. But at this stage we just want you to appreciate that even the relatively simple chemistry in aldeidoos chapter is useful in synthesis, in commerce, and in medicine.

Eventually 50 mg HCN per g of cassava can be released and this is enough to kill a human being after a meal of unfermented cassava.

But most larger more than four or so carbon atoms aldehydes and ketones are not. The solution is to make a bisulfite compound from it. You may ask how this is possible since dap- sone has no aldehyde or ketone—just two amino groups and a sulfone.

Reactividade de aldeídos e cetonas

There is also a change in oxidation state of the magnesium, from Mg 0 to Mg II. The ether solvent is essential for Grignard formation because 1 ethers unlike, say, alcohols or dichloromethane will not react with Grignards and, more impor- cetonxs, 2 only in ethers are Grignard reagents soluble.

We shall discuss the structure of glucose later in this chapter, but for now, just accept that it stabilizes the cyanohydrin. But it can matter to medicinal chemists, who make compounds alseidos need to be com- patible with biological systems.

Aldeidos e cetonas (1)

Secondary amines cannot form a neutral imine by loss of a second proton on nitrogen An enamine is formed instead. Bisulfite addition compounds Other compounds from cyanohydrins Cyanohydrins can be converted by simple reactions into hydroxyacids or amino alcohols.

Aldehydes and ketone react with HCN to form a cyanohydrin A catalytic amount of cyanide helps to speed the reaction. Ceyonas the compound will dissolve in water and release dapsone inside the patient. An aldehyde or ketone dissolved in an alcohol will form an equilibrium mixture containing the corresponding ladeidos.

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

Some people like eating these, but it is unwise to eat too many at one sitting! Aldehyde carbonyl groups are more electron deficient because they have only one electron-donating group attached to the carbonyl carbon. The hydrate is also called a gem-diol gem i. Dapsone is an antileprosy drug. 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.