Lab Report Assessment Answers

Subject Name : Chemistry

LAB REPORT
Contents
TOC o 1-3 h z u Experiment 1 Recrystallisation PAGEREF _Toc4865788 h 3Experiment 3 Preparation and reaction of an Alkene Elimination reactions of alcohols PAGEREF _Toc4865789 h 6Experiment 5 Halogen compounds synthesis of 4-methylbenzoic acid from a Grignard reagent classification of an unknown alcohol PAGEREF _Toc4865790 h 8Experiment 6 Aldehydes and ketones PAGEREF _Toc4865791 h 10Experiment 7 Reaction of an amine and a carboxylic acid derivative Preparation of Acetanilide PAGEREF _Toc4865792 h 12Experiment 8 Electrophilic aromatic substitution, substituent effects PAGEREF _Toc4865793 h 13

Experiment 1 RecrystallisationAbstract
The purification of the solid organic solvent is done with the process of recrystallisation with the help of appropriate solvent. The purity of the material later is established by comparison of melting point of the crystal formed with the known value of that particular compound. The underlying feature of this process depends on the fact that most of the organic compounds are soluble in hot solvents and the impurities present in the compound have different solubility than the desired component. Thus the effectiveness of this process depends on the selection of proper solvent. The good crystallization solvent can be confirmed if
the compound dissolves in the solvent in reasonable quantity at the boiling point,
the compound dissolves in very minute quantity at the low temperature
shows no reaction with the substance that is to be purified
dissolve the impurities at low temperature rapidly or does not at all dissolve it
solvent can be efficiently removed from the purified product
In case single solvent does not process all these properties the mixture of two solvents can be used (for example, water and ethanol)
Procedure
This involves six distinct processes
The impure material was dissolved in minimum amount of the hot solvent
The hot solvent is filtered in order to remove all the impurities
The solution was cooled so that the crystal compound gets deposited.
The crystal was filtered from the solution (mother liquor).
Further, the crystal was washed with help of cold solvent to remove mother liquor.
The dry crystal was removed from the last traces of the solvent
There are three major problems encountered during the process of recrystallisation that includes
The compound may crystallize in the filter paper during the process of hot filtration as the solubility of the compound decreases with decrease in temperature
The compound may not recrystallise due to presence of too much solvent and formation of supersaturated solution.
The compound may precipitate as oil as the compound having low melting point often turns into concentrated solution when above the melting point.
Results
compound number mass of the full tube mass of the empty tube
Evaluation of solvents for Recrystallisation
Water Ethanol Petroleum Ether
Soluble in cold solvent What happens on heating What happens on cooling Which solvent have you chosen for recrystallisation Why
Mass of the pure productMelting Point
Calculate the percentage recovery of pure product (based on your weighed amount of sample).
DISCUSSION
Even with perfect technique, it is never possible to recover 100 of the desired compound from a recrystallisation. Explain.
Answer. The recovery of the 100 of the desired compound is impossible as the chilled solvent remains saturated and are suppose to release some crystal. However, some of the desired material still remains dissolved in the cold solvent and it will be lost during separation of the crystal from the solvent. Thus the primary mass of the compound is lost into the solvent.
Why, in principle, should the minimum volume of solvent be used
Answer. It is necessary to use minimum amount of the solvent in recrystallisation process because the compound may remain dissolved even after the cooling of the solvent.
Why, in practice, do we use 10 - 20 more than the minimum volume of solvent
Answer. In practice 105 to 20 more than the minimum volume is required so that the hot solution would not remain quite saturated. This also helps in avoiding the crystal formation during cooling which may result in clogging the pores of filter paper.
The three compounds depicted in the graph shows difference in solubility of the compound at different temperature. Here, solvent B is most suitable as the compound can be heated into this solvent till the boiling temperature, further on cooling the dissolved compound will start recrystallisation. Thus the compound of interest can be obtained while the other compound will remain dissolved in the solvent. The solvent A is most inappropriate as this does not dissolve the solvent rapidly at appropriate temperature.

Experiment 3 Preparation and reaction of an Alkene Elimination reactions of alcoholsAbstract
The formation of new carbon-carbon bond compound can be formed with help of elimination. The usual catalysts involved are high-boiling mineral acids such as sulfuric or phosphoric acid. The use of the catalyst have role in formation of the protonoted alcohol. At the temperature of 50 and 150 C, a molecule of water is eliminated from the protonated alcohol in order to give carbocation. However, this process is unstable in nature and results in formation of alkenes. Further the removal of the alkene from the mixture leads to shift in the equilibrium to shift from right and results information of more alkene. Thus, alternatively more alkene is formed by addition of more water.
Procedure
The problems in this experiment include presence of concentrated sulfuric acid that may cause serious burns to eyes or skin.
The methanol used may act as irritant in skin, eyes, or cause respiratory irritation.
The methane used is flammable in liquid and vapors
Results
Part A dehydration of Menthol
mass of menthol used 2 g, 20 mmol
mass of menthene obtained
boiling point range of menthene
Boiling point of methane reported in the literature 176 C
Write your literature reference for your boiling point below.
Answer.
PART B characteristic reactions of hydrocarbons
Cyclohexane cyclohexene menthene
reaction with 0.5 KMnO4 solution
reaction with Br2/ H2O
Discussion
Using structural formulae, write a balanced equation for the dehydration of menthol
Answer.

Calculate the theoretical yield of menthene for your part A, and the yield you obtained
Answer.
What factors, based on their molecular structure, contribute to the large difference in boiling point between menthol and menthene
Answer. The structural formula that contributes to the large difference in the boiling point of methane and menthene includes difference in the number of carbons and differnace in branching. The presence greater number of the carbon and less branching increases the boiling of the menthol while presence in less number of the carbon atoms and more branching decreases the boiling point of the menthene.
Using structural formulae for the organic products, write equations for the reactions your menthene sample underwent in part B. How did these reactions help you characterise your product as menthene
IR spectra
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Experiment 5 Halogen compounds synthesis of 4-methylbenzoic acid from a Grignard reagent classification of an unknown alcoholAbstract
The experiments show that Grignard reagent belongs to the group of versatile synthetic reagents and thus are able to readialy form bromoalkanes or bromoarenes. Moreover, Grignard reagent reacts more readily with bromo compound rather than chloro compound. This experiment uses p-tolylmagnesium bromide that is responsible for the addition of carbon di oxide in order to give magnesium bromide (salt) of the corresponding compound used in the experiment. The acidification of the magnesium bromide salt resulted in yielding of the 4-methylbenzoic acid.
Procedure
First problem encountered in this case involves composition of the Grignard Reagent in the ether solvent. The second problem involves mechanism by which the reagents react with the other groups. Thirdly, the problem encountered while performing this experiment was separation of the mixture of the compounds into single compound and the step that is involved in the purification and the identification of the compound.
Results
The preparation and characterisation of 4-methylbenzoic acid
Volume of 0.5 M 4-tolymagnesium bromide solution used
mass of 4-methylbenzoic acid obtained
m.p. of 4-methylbenzoic acid reported in the literature
DISCUSSION
Based on the theoretical yield determined in the prework, calculate the yield of 4-methybenzoic acid you obtained
Answer.
Write a balanced equation (using structures) for the reaction that occurs when the ether solution of the reaction product is extracted with sodium bicarbonate solution.
Answer.
Following from q.2, write a balanced equation for the reaction of the aqueous layer with 5M HCl.
Answer.

Experiment 6 Aldehydes and ketonesABSTRACT
The experiment depicts that the aldehydes and ketones undergo similar type of the reaction however, the reaction is little faster in case of the aldehydes due to less crowding of the carbonyl carbon compound. The first part involves reaction of ketone with sodium borohydride while the second reaction involves reaction of an aldehyde with primary amine. Moreover, most of the carbonyl reactions occurs with both aldehydes and ketones
PROCEDURE
The major problem encountered in this case is elimination of overoxidation with the reaction of primary alcohol as the aldehydes are easily oxidized to acids. Moreover, in the first part the sodium borohydride required to be handled carefully as this may cause severe irritation in the eyes.
RESULTS
DISCUSSION
Questions for Part A
Balance the equation below for the reaction of benzil with sodium borohydride (reading the Introduction will help).
Answer.

Calculate the number of moles of sodium borohydride and benzil used in the experiment. Taking into account the balanced equation, which of these is the limiting reactan
Calculate the number of moles of sodium borohydride and benzil used in the experiment. Taking into account the balanced equation, which of these is the limiting reactant
Calculate the percentage yield of hydrobenzoin you obtained in Part A
How many stereoisomers of hydrobenzoin are there altogether Why
Answer. The total numbers of the stereoisomers in case of hydrobenzoin are three. In the reaction there are two chirality centers. The possible number of steroisomer that can be formed due to two chirality centers will be four. However, in this case the two chirality centers exactly posses four groups, which is a meso form is possible. Thus on reduction of benzyl, it possesses three steroisomers.
Based just on the reactants used, could your product be optically active Explain briefly.
Answer. No, the product obtained from the used reactant could not be optically active in nature. The reactant used in this reaction was optically active. Thus when the reaction takes placethe enantiomers possesses equal and opposite rotation, in other words, the reaction results in formation of racemix mixture which is not optically active in nature.

Experiment 7 Reaction of an amine and a carboxylic acid derivative Preparation of Acetanilide
ABSTRACT
The carboxylic acids, ester, amides, anhydrides, and acid chlorides are grouped under the category of carboxylic acid derivation. This experiment illustrates interconversion of carboxylic acid derivates from ketones and aldehydes.
PROCEDURE
One of the potential problems encountered in case of acetanilide is its rapid recrystallisation from the boiling water. The product requires washing multiple numbers of times with crude acetanilide as well as water. Another, potential problem that may be caused in this experiment may be due to improper handling of the acetic anhydride in the conical flask.
RESULTS
Discussion
Write a balanced equation, using structural formulae, for the reaction of aniline with acetic anhydride to form acetanilide.
Answer. NH4CNO_____ HeatNH2CONH2
Rearrangement
C3H7NO2 C4H6O3 C8H9NO

Calculate the yield of acetanilide you obtained.
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Experiment 8 Electrophilic aromatic substitution, substituent effectsAbstract
This experiment shows that benzene undergoes substitution reaction. The first step (slow process) follows addition of an electrophile to the ring that result in formation of carbocation intermediate. The second step (rapid reaction) involves losing of proton from carbocation intermediate and restoring of the aromatic ring.
Procedure
The main concern encountered in this experiment involves separation of the isomer mixture. The adequate separation of this mixture involves setting of adequate melting point for the purpose of the separation. Another important problem invoves possibility of carbocation rearrangements when there is requirement of addition of more than two carbons in the carbon chain. The main cause of this rearrangement is hydride and methyl shifts.
RESULTS
What is limiting reactant
The limiting reactant is referred to the chemical reaction that limits the amount or the volume of the product formed. The ongoing reaction generally stops when the limiting product is completely consumed.

Calculate the theoretical yield of bromoacetanilide.
The theoretical yield of bromoacetanilide reaction involves
Molecular formula of acetanilide C8H9NO
Molecular formula of p-bromo acetanilide C8H8NOBr
Weight of acetanilide 135 g/mole
Weight of p-bromo acetanilide 214 g/mole
Theoretical yield of the product will be
135 g of acetanilide gives 214 g of p-bromo acetanilide
Therefore, 10 g of acetanilide would give X g of p-bromo acetanilide
X 21410/135 15.85 g
Since, the practical yield of the product is 10g,
Therefore, the yield of the product will be equivalent to
Yield Practical yield/ theoretical yield 100
10/ 15.58 63.09
DISCUSSION
Compare your experimental melting point with the published values above. Which isomer of bromoacetanilide have you prepared State any assumptions you have made.
Using the results you obtained in Part B of this experiment, arrange the following substituents in decreasing order of ring activation for electrophilic aromatic substitution NHCOCH3, CH3, OCH3, OH, NO2, H, Cl, NH2.
Explain how your results in part B tell you whether the nitro group is activating or deactivating.
Following from q3, explain what you can conclude about activating/deactivating substituents from the reaction times you observed for p-chlorophenol