ester

Examples of ester in the following topics:

• Esters

  • Esters are ubiquitous.
  • Polymerized esters, or polyesters, are important plastics, with monomers linked by esteric units like this:
  • Ester names are derived from the parent alcohol and acid.
  • Cyclic esters are known as lactones.
  • Esters react with nucleophiles at the carbonyl carbon.

• Reactions of Alkylidene Complexes

  • Since the carbene moiety of a Fischer carbene has many of the characteristics of a carbonyl group, it is instructive to begin our survey with some ester-like transformations.
  • The first diagram displays a few carbonyl-like reactions, which mimic organolithium addition to ketones (eq. # 1), ester amination (eq. # 2), the Wittig reaction (eq. # 3) and alpha-carbon alkylation (eq. # 4).
  • In most cases the carbene is a stronger activating group than the corresponding ester.
  • The last equation shows an unusual case of thermal [2+2]-cycloaddition, which does not take place with the ester equivalent.

• Claisen Condensation

  • Esters undergo a similar transformation called the Claisen Condensation.
  • Greek letter assignments for the ester products are given in blue.
  • The specific alkoxide base used should match the alcohol component of the ester to avoid ester exchange reactions.
  • Esters usually serve as the electrophilic acceptor component of the condensation.
  • There are three ester functions, each of which has at least one alpha-hydrogen.

• Reactions with Organometallic Reagents

  • Esters are the most common carbonyl reactants, since they are cheaper and less hazardous to use than acyl chlorides and anhydrides.
  • Most esters react with organometallic reagents to give 3º-alcohols; but formate esters (R=H) give 2º-alcohols.
  • The second equation demonstrates the low reactivity of organocadmium reagents, inasmuch as the ester function is unchanged.
  • Esters react with organometallic reagents to give 3º-alcohols; formate esters (R=H) give 2º-alcohols
  • Reaction with acyl chlorides, anhydrides and esters leads to alcohol products

• Waxes

  • Natural waxes are typically esters of fatty acids and long chain alcohols.
  • Animal wax esters are typically derived from a variety of carboxylic acids and fatty alcohols.
  • A major component of beeswax is the ester myricyl palmitate , which bees use for constructing honeycombs.
  • One of its main constituents is cetyl palmitate, an ester of a fatty acid and fatty alcohol.
  • Unlike most natural waxes, which are esters, synthetic waxes consist of long-chain hydrocarbons lacking functional groups.

• Waxes

  • Waxes are esters of fatty acids with long chain monohydric alcohols (one hydroxyl group).
  • Natural waxes are often mixtures of such esters, and may also contain hydrocarbons.

• Nucleophilicity of Phosphorus Compounds

  • The chemistry of phosphines and the related phosphite esters is dominated by their strong nucleophilicity and reducing character.
  • Phosphite esters react in the same manner, but the resulting phosphonium salts (shaded box) are often unstable, and on heating yield dialkyl phosphonate esters by way of a second SN2 reaction (equation 2 below).

• Enolate Intermediates

  • Esters and nitriles are even weaker alpha-carbon acids than ketones (by over ten thousand times), nevertheless their enolate anions may be prepared and used in a similar fashion.
  • Malonic acid esters and acetoacetic acid esters are commonly used starting materials, and their usefulness in synthesis will be demonstrated later in this chapter.

• Related Carbonyl Derivatives

  • Most of the functions are amides or esters, cantharidin being a rare example of a natural anhydride.
  • Cyclic esters are called lactones, and cyclic amides are referred to as lactams.

• Acyl Group Substitution

  • Reactivity: acyl halides > anhydrides >> esters ≈ acids >> amides
  • The reaction of an acyl chloride with an alcohol also gives an ester, but this conversion cannot be reversed by adding HCl to the reaction mixture.
  • Esters are one of the most common carboxylic derivatives.
  • Finally, anhydrides and esters have intermediate reactivities, with anhydrides being more reactive than esters.
  • Esters are less reactive acylating reagents than anhydrides, and the ester exchange reaction (#6) requires a strong acid or base catalyst.