Objectives

You will do an acid-catalyzed esterification reaction to make a common ester existing in countless different fruits. This ester, isopentyl acetate is just one of the chemistry in bananas. Using typical laboratory procedures, you will isolate and characterize your product. Originally a reflux will allow the reaction to continue for about an hour. The product the reaction will be built up following a straightforward distillation, washed and also dried prior to isolating that in much more pure type in the next lab. Her product will be gathered and analyzed using IR, refractive index, density, etc.

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Background

Esterification is astraightforward reaction that uses several crucial techniques insynthetic essential chemistry. One direct approach, well-known as the Fischeresterification reaction, entails the acid-catalyzed condensation that analcohol and a carboxylic acid, yielding one ester and also water. Esters canalso be created by the reaction of the alcohol v the mountain chloriderather 보다 the acid itself. Or, the acid anhydride might be supplied insteadof the acid. In this experiment, we will produce the ester isopentylacetate (banana oil) via the Fischer esterification reaction.

Esters are critical groupof carboxylic mountain derivatives. Many esters occur naturally. They oftencompose a far-ranging fraction the the fragrant oil of fruit andflowers. Fats and also oils are another type of natural ester; they areactually mixture of glycerol triesters, do of long-chain fat acidsand glycerol (glycerin: 1,2,3-propanetriol). Waxes are esters oflong-chain carboxylic acids and also long-chain primary alcohols. Lactonesare cyclic esters the arise once a carboxyl group and also an alcohol groupin the same molecule condense to form an ester. Fabricated esters arealso important and also found in countless places, consisting of the polyesters knownas Dacron, ready from terephthalic acid and ethylene glycol, andKodel.

Emil Fischer (1852-1919) to be aGerman scientist who received his Ph.D. From the university ofStrasbourg, examining with Adolf von Baeyer. He taught at Erlangen,Wurzburg, and also Berlin Universities. Fischer"s work essentially laid thefoundation of modern-day biochemistry. Fischer was the first to synthesizephenylhydrazine, i m sorry was vital reagent in his work-related onelucidating the structures of most of the carbohydrates. During athree-year period beginning in 1891, Fischer created not just thebasic structures, but additionally the construction of every the known sugars.In the process, he developed a technique to represent thethree-dimensional molecular structures in two-dimensional drawings.These structures have end up being known as Fischer forecast formulas. Thiswork through Fischer led directly to prove the visibility of the asymmetriccarbon atom, a concept proposed by Van"t Hoff and Lebel in 1874.

In enhancement to carbohydratechemistry, Fischer did considerable work on the chemistry of purine andcompounds having purine as their nucleus. Purine is one of the twonitrogen basic ring systems existing in DNA.

Fischer to be also energetic in thearea that protein chemistry. He demonstrated that amino acids space thebasic subunits indigenous which proteins room constructed. He also devisedmethods because that the synthetic of countless of the well-known amino acids. Probably hismost ingenious contribution was the "lock and also key" hypothesis of howproteins bind through substrates of safety shapes. This workultimately led to our knowledge of just how enzymes, the catalysts ofbiochemical reactions, function.

Regarded as the greatestorganic chemist of his time, Emil Fischer became the 2nd chemist toreceive the Nobel compensation (1902). Fischer committed suicide in 1919following the death of his wife and also the ns of 2 of his three sons.

The Fischer esterification isan equilibrium reaction whereas various other esterification routes execute notinvolve one equilibrium. To shift the equilibrium to donate theproduction that esters, it is customary to usage an excess of one of thereactants, either the alcohol or the acid. In the existing reaction, wewill be utilizing an excess of the acetic acid, due to the fact that it is cheaper andeasier to eliminate than the alcohol (note the comparable boiling points ofthe alcohol and also acetate). Another method to drive a reaction toward itsproducts is come remove among the products as the forms. In thisexperiment, us will eliminate the water formed in the reaction through addingsilica beads directly to the reaction vessel and by making use of a dry tubewith drying agent (calcium chhioride), which prevents the introductionof water.

The following number shows thereaction because that this experiment:

*

The system for this reactioninvolves the nucleophilic enhancement of the alcohol come the carbonyl groupof the protonated acid, followed by removed of a proton. Thetetrahedral intermediary is stormy under the acidic conditions of thereaction and undergoes dehydration to form the ester.

The crucial steps the this mechanisminvolve the following:

Activation of the carbonylgroup by protonation the the carbonyl oxygen, Nucleophilic addition to theprotonated carbonyl to type a tetrahedral intermediate, removed of water native tetrahedral intermediary to regain the carbonyl group.

Because esters deserve to behydrolyzed under acidic or straightforward conditions, that is no a an excellent idea tostop this reaction before the acid catalyst has actually been neutralized.Hydrolysis is the break of the ester apart back to the acid and thealcohol. This reaction can be useful; if the hydrolysis is carried outunder simple conditions, it is referred to as a saponification.Saponification is one irreversible reaction in i beg your pardon one mole of base isconsumed every mole that ester to generate the carboxylic acid anion.

Procedure

Assemble the adhering to apparatus:

A 100-mL round bottom flask, comprise a little clam-shell-shaped stirring bar attach a water condenser shaft for reflux. Tubing to cool the condensor shaft is fastened so that the water enters the pillar at the reduced nipple and exits the top nipple connector. The water condenser is topped v a calcium chloride drying tube. (The drying tube is assembled by first placing a small amount glass wool right into the pipe in order come cover the bottom opening. Include enough anhydrous CaCl2 come about fifty percent fill the dry tube. Insert the bottom nipple that the drying tube into a #1 one-hole rubber stopper, i m sorry is then inserted into the top of the condensor.)

The apparatus will certainly be heated using a heater manifold put on height of a stirring warm plate (hot plate is not offered to administer heat, only to row the components of the reaction flask). Secure the reaction setup come a ring stand using a 3 prong clamp attached to the condenser column, so that the reaction courage (after the reaction is completed) deserve to beeasily elevated and cooled in the air.

The reaction materials are included as follows.

include 20 mL the isopentyl (isoamyl) alcohol come a 100-mL round bottom flask include a clam-shell-shaped stirring bar include 12 mL of glacial acetic acid to her round-bottom flask with the alcohol and stirring bar Add around 1 mL of concentrated sulfuric mountain (use a disposable plastic pipet which has actually an almost right 1-mL marking on it straight into her round bottom flask (do not shot to measure up the sulfuric mountain in a graduated cyclinder) Finally, add around 1.5 g (about means 1 gram is ok, and also 2 grams is ok) that silica gelatin beads (8 mesh dimension with indicator (indicator should be blue denote anhydrous); no powdered silica gel) to the flask. The reaction flask is heatedusing reflux for around 60 minutes. (Start timing once your reactionmixture has begun to boil)

after the 60-minute reactionis complete, turn off the heating mantel and also elevate the reaction flask to permit it come cool come room temperature.

very closely decant (pour) the liquidpart of the reaction container making use of a funnel right into a Separatory Funnel (make certainthat the silica gelatin beads and also stirring bar continue to be in the reactioncontainer). Remove the stirring bar and also discard the silicagel beads right into the solid waste container.

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Isolation the Product:

After your reflux is finished,and the liquid reaction mixture has actually been included to the SeparatoryFunnel, you will should do washes to neutralize the sulfuric andacetic mountain in the mixture. To carry out these washes, usage three20-mL portions of 5% sodium bicarbonate which will certainly neutralize the acidin the mixture. The separatory funnel is capped and also thenshaken vigorously, with constant venting (carbon dioxide gas isproduced). After each of the 3 washing steps, permit thelayers separate and then remove and discard the lower aqueouslayer. The top layer will certainly be her isopentyl acetate and also thelower layer will be the aqueous bicarbonate and water layers arecollected into another flask and eventually discarded in liquid waste.

The bicarbonate washings the theester product are followed by a solitary 20-mL wash using distilled water toremove any bicarbonate ion that might still be combined withproduct. ~ the water class (bottom layer) is removed, the isopentylacetate is transferred to one 100-mL ring bottom flask (use 19/22 soil glass flask).

Your accumulated isopentyl acetate need to be dried making use of a dehydrating agent. You should use anhydrous salt sulfate (Na2SO4) come dry your chemical. Add about 2 grams of the anhydrous salt sulftate (this amount of anhydrous salt sulfate is sufficient to tie over 2.5 grams of water).

Store your liquid product, withdrying agent, until the next lab period. Prior to distillation of your product during the 2nd day, theanhydrous isopentyl acetate is very closely poured or decanted far from the solid salt sulfatein the drying flask. Put your dried ester into a clean, and also dry, 50- or 100-mL ring bottom flask fordistillation.

PURIFICATION:

Purification ofthe rudely isopentyl acetate is carry out by distillation. Theentire product is added to a 50-mL round bottom flask, containingseveral boil stones to protect against super-heating and bumping that thecrude isoamyl acetate during distillation. A simple distillation isperformed to collect the isoamyl acetate. The flask is heatedin utilizing a heating manifold. The isopentyl acetate will boiland condense and also will be collected. This distillation willsignificantly wash the material, but not if over there is alcohol or waterpresent. You have to collect your material when you have actually aproduct in ~ the suitable boiling allude of the ester.

CHARACTERIZATION:

The boilingpoint that the liquid have to be measured as the isopentyl acetatedistills. The thermometer is placed in the distillation head.A many of warmth is lost to the environment when utilizing this verysmall equipment, so a thermometer inserted in the distillation head is apretty an excellent indicator the the cook point.

An analysis of her productshould incorporate the following:

Boiling point Actual yield Percent productivity IR sprectrum GC chromatograph for purity Refractive index

The spectra space the IR"s forisopentyl alcohol (isoamyl alcohol) and isopentyl acetate (an ester).