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Experiment 1 Title: Acid-Based extraction Objective: To learn the concept of separating organic compounds by utilizing the concept of acid/base chemistry in so that separation can be done. Introduction: Acid-base extraction is a procedure using sequential liquid-liquid extractions to purify acids and bases from mixtures based on their chemical properties. Benzoic acid, C7H6O2 (or C6H5COOH), is a colorless crystalline solid and the simplest aromatic carboxylic acid. Benzoic acid has density of 1.23g/ml which are denser than water. Organic acids and bases can be separated from each other and from neutral compounds by extraction using aqueous solutions of different pH. Most organic acids (e.g., carboxylic acids) are insoluble or slightly soluble in water, but these compounds are highly soluble in dilute aqueous sodium hydroxide because the organic acid reacts with the base. -

+ NaOH

Na+ (water soluble salt) + H2O

Benzoic acid Thus, the acid may be selectively removed from a mixture by dissolving the mixture in an organic solvent and then extracting the solution with dilute sodium hydroxide. The organic acid may be recovered from the aqueous solution by acidification, which causes precipitation, followed by filtration.

-

Na+ + HCl

+ NaCl

A drying agent is an inorganic salt which readily takes up water to become hydrated. Drying agent

Capacity

Speed

Applications

calcium chloride, CaCl2

high

medium

used for hydrocarbons

fast

generally useful

calcium (Drierite)

sulfate,

CaSO4 low

magnesium sulfate, MgSO4

high

fast

not used for compounds

very

potassium carbonate, K2CO3

medium

medium

not for acidic compounds

sodium sulfate, Na2SO4

high

slow

generally useful

acid-sensitive

Of the five drying agents in the above table, magnesium sulfate is a fine powder and the rest are of a larger particle size. Calcium chloride, magnesium sulfate, and sodium sulfate are the three most commonly used agents.

Procedure: 1. Extraction: i. 0.24grams of unknown sample and 0.12 grams benzoic acid was weight and placed in a test tube. ii. 10ml of ether was added to the mixture and was shakes to dissolve the mixture. iii. The solution then transferred to separatory funnel and 5ml of 1M NaOH was added, with the cap tight, the layers was mix by swirling and shaking for 30 minutes. Pressure was vent by titling the funnel and opening the stop cork. iv. It was shakes again after closed the stop cork. The mixture was leaved to stand to allow the layers to separate. The aqueous layer was drain into Erlenmeyer flask and was labeled as first extraction NaOH. v. 5ml of the 1M NaOH solution was added to the ether layer in the funnel and the step i-iv was repeated and labeled as second extraction NaOH. 1. Filtration i. The flask was taken to the hood and by using glass rod slowly stirring when 6M HCl was added into each Erlenmeyer flask until the solution was acidic by using blue litmus paper. ii. The flask then was taken to cool in an ice bath for about 15 minutes or until thoroughly chilled. iii. The solid benzoic acid was collected using Buchner funnel and filter flask. iv. 2-3ml water was used to wash and allowing the suction to continue for five minutes to get solid as dry as possible. v. It was scratched gently into watch glass and was put into oven for complete dryness. vi. The solid was weight and obtain melting point. (Optional) 1. Remove NaOH i. 5ml or saturated solution of sodium chloride was added to the ether layer in separatory funnel ( this is to remove any trace of NaOH solution) ii. The layer was separated like before by cap, mixed and vent. iii. The ether layer was transfer into an Erlenmeyer flask and 1 g of anhydrous sodium sulfate was added to remove the moisture (water) it contains. iv. The stop cork was closed and swirled and was leaved to stand for 10 minutes v. While the ether layer was drying, a small beaker or Erlenmeyer flask was weight. vi. The dried ether layer was transfer using Pasteur filter pipette into a beaker. ‘ vii. The beaker then brought to steam bath in the fume hood to evaporate the ether. viii. After evaporated, the beaker was cool at room temperature and was reweighting to determine the yield of the unknown sample. ix. The melting point was obtained and compared to the two chemicals given.

Result and Observation:

Actual weight of unknown

0.2435g

Weight of unknown recovered

0.1917g

Calculation: Benzoic acid:-

122.4oC

Melting point of unknown

Filter paper: 2 pieces x 0.341g = 0.682g Watch glass: 42.867g

Color

white

Actual weight of benzoic acid

0.1218g

Extraction NaOH (after drying) = 43.640g – 43.549g = 0.091g Percent of benzoic acid recovered = (recovered weight / actual weight) x 100

Weight of benzoic acid recovered -Before drying -After drying

Extraction NaOH (before drying) = 45.446g – 43.549g = 1.897g

= (0.091g / 0.1218g ) x 100

1.897g 0.091g 165oC

Melting point of benzoic acid

= Color

Light pink

74.7% Unknown Sample:Flask: 46.7520g

Flask + Unknown sample: 46.943g Unknown = 46.9437g – 46.7520g = 0.1917g Percent of Unknown recovered = (recovered weight / actual weight) x 100 = (0.1917g / 0.2435g) x 100 = 78.7% Melting point: (173oC + 160oC) / 2 = 166.5oC Discussion: From the result of finding the melting point of the unknown sample is 166.5oC which was at the range of triphenylmethanol, however the literature melting point of triphenylmethane is 163oC.

The reason why it was more than literature melting point is maybe it still contain of water or ether, where it may effect during finding the melting point. Other reason maybe because of using melting point apparatus that still hot used before us. From the result and calculation also shows that the percent of recovered of benzoic acid and unknown (triphenylmethanol) was not 100%, which are 74.7% and 78.7% respectively. This may cause during the extraction and filtration. The solution was not fully extract by NaOH or/and the extraction was not fully acidic before leave it to cool. If NaOH was not fully separate the benzoic acid with water, then maybe there are some benzoic acid left. In the other hand, if the extraction of NaOH was not fully acidic before cool, it would not fully recrystalization. The techniques of using vacuum filtration also matters, where some of the solution may not pass through the filter paper. Same with the tryphenylmethane solution, where the drying agent that is anhydrous sodium sulfate was not fully absorbed the water contains. Furthermore, we saw the anhydrous sodium sulfate bottle was leave to open, this can cause the ineffectiveness of the drying agent. Mean that although the ether was fully vaporized, there still water remain which cannot be evaporate along with the ether, this is because water have higher boiling point than ether (35oC). The solution of extraction of NaOH was in pink color, makes the crystal in pink color also, this is because of the effect of the litmus paper which blue litmus paper turned to red to show the acidity of the extraction of NaOH. It will not affect the recrystilization product. Triphenylmethanol (also known as triphenylcarbinol) is an aromatic organic compound. It is a white crystalline solid that is insoluble in water and petroleum ether, but well soluble in ethanol, diethyl ether and benzene. It has density of 1.199g/cm3.

Structure of triphenylmethanol

Conclusion: The experiment involve of extraction and vacuum filtration technique, which the perfection of the techniques do matters. However as human being, we do some mistakes that cause error or not get the most precise percentage of recovered.

We obtain 74.7% of recovered benzoic acid and 78.7% of recovered unknown solution. We identify the unknown solution by comparing the melting point we obtained with the literature melting, the unknown solution is Triphenylmethane.

References: Extraction Experiment Retrived on January, 17 2010 from http://chemistry.csudh.edu/faculty/noel/CHE317L/Extraction%20Experiment_files Jerry Manion. (1997)Modular laboratory program in chemistry - Separating Acid and Neutral Compound by Solvent Extraction. H.A Neldig. Arkansas Triphenylmethane Retreived on January, 26 2010 from http://en.wikipedia.org/w/index.php? title=Triphenylmethanol CUBoulder Organic Chemistry Undergraduate Courses – Drying Organic Solutions. Retrieved on January, 17 2010 from http://orgchem.colorado.edu/dryingorganicsolution

Questions: 1. List four water-immiscible liquids other than ether that could be used to extract organic compounds from equeous solution. i. Methylene Chloride (dichloromethane) ii. Chloroform(trichloromethane) iii. Carbon tetrachloride (tetrachloro-methane) iv. Cyclohexane 1. Why is it wrong to leave a bottle of anhydrous sodium sulfate or calcium chloride open? The air contain of water, when open the bottle of anhydrous, it expose the anhydrous to absorb the water particles in the air, this will affect the anhydrous effectiveness during experiment. 2. Draw the structure of the product when benzoic acid reacts with sodium hydroxide. Why is the product of this reaction easily extracted into H2O, while the original benzoic acid is not so easily extracted into H2O?

This is because the stronger OH-, removes a hydrogen H+ to form a salt, the polar salt is soluble in aqueous solution, both OH- and benzoate are bases, the stronger base takes H+ from the weaker base. 3. Why does benzoic acid precipitate out when the aqueous layer is acidified with HCl? Because the benzoic ion is stronger bases than Cl-, so each one takes H+ from HCl, the acid forms are not water soluble, so they precipitate out from solution.

4. Develop a procedure for isolating a neutral compound from a mixture containing a basic impurity by drawing a flow chart as on page 20.

Benzoic acid and triphenylmethane

Ether p-chloroaniline naphthalene Extract with HCl ( 2 times) Combined water layers naphthalene

Amine hydrochloride salt

trace of HCl Extract with water

add concentrated NaOH water Small amount of HCl

ether naphthalene

(discard)

p-chloroaniline (solid) (discard)

Dry (sodium sulfate) evaporate naphthalene