Oxidation of toluene by potassium permanganate

Introduction

Benzoic acid is a versatile reagent that can be implemented in a plethora of syntheses (e.g. benzene [Ref. 1], methyl benzoate [Ref. 2], etc). Today, benzoic acid is most commonly encountered as benzoate due to food  its preserving properties[Ref 3.]. Benzoic acid can be prepared in the home lab through the oxidation of toluene using Potassium Permanganate. Interestingly, Potassium permanganate can oxidise any alkyl benzene so long as it contains a benzylic hydrogen. The mechanism not completely understood, however it is thought that potassium permanganate abstracts a hydrogen forming a radical, although the rest is not known[Ref. 4][Ref. 5] The scheme is given below:

  Reaction equation: 

C₆H₅CH_{3 (aq)} + 2 KMnO_4(aq) → C₆H₅COOK(aq)+ 2 MnO₂(S) H₂O(aq)+ KOH(aq)

In this experiment we will make Benzoic acid via oxidation by potassium permanganate 

Purpose

To synthesise Benzoic acid on a laboratory scale.

Safety and Disposal: 

Before attempting any experiment be sure to read all relevant safety information on the chemicals you will be handling/producing. In this experiment it is highly recommended to wear gloves, wear eye protection, wear a lab coat and work in a well ventilated area (preferably out side or in fume hood). Concentrated Hydrochloric acid is highly corrosive along with its fumes. Potassium permanganate is highly oxidising and stains everything. Toluene posses an inhalation hazard, and is toxic.Benzoic acid is not particularly toxic, however exposure should be limited. Be sure to read all relevant disposal regulations, as it different depending on where you live the and author can't give such information. The author of this blog will not be held responsible for any damage caused by following directly or indirectly instructions/ gaining information from this blog. 

Note: this experiment was based on the procedure found here: http://en.wikibooks.org/wiki/Applied_Science_BTEC_Nationals/Chemical_Laboratory_Techniques/Benzoic_acid

Procedure

Weigh out 8.00 (50.622 mmol)grams of potassium permanganate and add to the round bottom flask

To the Round bottom flask add 90 ml of distilled water and 4.664 (50.622 mmol) grams of toluene (~10 ml) (note*) add a magnetic stir bar, fit the reflux condenser and begin water flow (thermometer not necessary)

Reflux the solution for 2-2.5 hours with vigorous magnetic stirring

as the reaction progresses the intense purple permanganate ion will gradually disappear as it is reduced from manganese (VII) to manganese (IV) which precipitates as brown manganese dioxide 

After 2.5 hours the reflux was stopped and the manganese dioxide was vacuum filtered with a Buchner funnel (do not wash the precipitate) 

 

The filtrate was put into a small separatory funnel and the aqueous phase was drained into an appropriately sized beaker.

The aqueous layer was then acidified with excess (until no more precipitate forms) conc. hydrochloric acid. 

The benzoic acid precipitate was vacuum filtered and washed with ~ 2x 60 ml distilled water. (note** ) The precipitate was pressed with a glass stopper until no more mother liquor passed through the filter frit. Air was then drawn though the product until dry.

Notes

note*:the required amount of toluene is 25.31 mmol, however the reaction works best with toluene in excess, as this allows for a greater phase boundary surface area, as toluene is not very soluble in water (0.52 g/L (20 °C)). It also eliminates a step in the original procedure to reduce any remaining permanganate ion. 

note**: this proved to a possible cause for low yield. 2x 30ml with ice cold distilled water seems to be more appropriate and would result in less product loss. However, it could be suggested that if the mother liquor was boiled down to less than half its volume and placed in an ice bath, some of the product could be recovered.

Conclusion

The aim of the experiment was achieved; benzoic acid was prepared on a small scale. Although the product has not been characterised due to lack of resources, a qualitative test can be carried out using a soluble copper (ii) salt to form the benzoate which precipitates out of solution. Yield was ~ 2 grams or a ~32% yield. This is most likely due to the over oxidation of toluene to carbon dioxide, small scale and mechanical losses. However, as discussed in note**, some of the product may be recovered from the washes. On a larger scale a better yield should be obtained.
References
[Ref.1] James F Norris, JFN (1924), Experimental Organic Chemistry, Second Edition,  MCGRAW-HILL BOOK COMPANY, INC, USA 

[Ref. 2] Arthur I. Vogel, AIV (1948), Practical Organic Chemistry, Third Edition,  LOWE AND BRYDONE (PRINTERS) LTD, GBR

[Ref 3.] http://pubchem.ncbi.nlm.nih.gov. 2004. Compound Summary for: CID 243 Benzoic Acid. [ONLINE] Available at: http://pubchem.ncbi.nlm.nih.gov/rest/chemical/benzoic+acid. [Accessed 31 August 14]. 
[Ref.4] Master Organic Chemistry. 2012. Oxidation of aromatic alkanes with KMnO4 to give carboxylic acids. [ONLINE] Available at: http://www.masterorganicchemistry.com/reaction-guide/oxidation-of-aromatic-alkanes-with-kmno4-to-give-carboxylic-acids/. [Accessed 31 August 14].

[Ref. 5]Sukalyan Dash , Sabita Patel , Bijay K. Mishra ,(2008), Oxidation by permanganate: synthetic and                   mechanistic aspects, Tetrahedron, 65(4), 724

Quick post: How to make a steel spatula

Construction of a steel laboratory spatula.


Introduction.

Laboratory spatulas are useful instrument in any scientific setting. They are an excellent tool for transferring small quantities of reagents, scratching the sides of a flask to induce crystallisation and can be used as a platform for the deflagration of small amounts of pyrotechnic mixtures. Although cheap, finding high quality lab spatulas can, for some, be difficult and often through international sources, which entails shipping rates etc. This report will demonstrate the simplicity of designing and building one's own spatula for minimum costs at home.

Purpose

To built a laboratory spatula with minimum funds.

Materials

- 2 mm steel wire (free)
- butane torch (already had)
- hammer (already had)
- hard steel surface [anvil or bench vice] (already had)
- file(already had)
- sand paper, steel wool and or sanding sponge (already had)
- safety glasses and heavy duty gloves (already had)

Safety considerations

Because steel will be heated to high temperatures, caution must be used when handling the hot material. Keep a burn relief kit nearby and wear safety goggles and heavy duty gloves to protect from burns. Do this in a well ventillated area!

Procedure

1.Measure out about 18.5 cm of the steel wire.


2. Begin heating with the torch until you obtain a cherry red, then begin hammering and flattening out the end of the wire (until roughly ~2 cm has been flattened)
 
3.A technique known as "hot filing" maybe implemented to shape the spatula. Heat the end and start filling. Use caution. It is useful to thin out the spatula a little at this point.


4.Once the final shape has been achieved, heat the end of the spatula and quench it to harden the tip.


5.Repeat steps 1-4 for the other side with the desired shape.

6.Once hardened, the work up of the spatula may begin. use rough sand paper, then go to a finer grade and finish with a sanding block.


Discussion

The spatula came out with very satisfactory results. The main limitations of the spatula is that it is not stainless steel, hence it is mainly useful for only rough qualitative work and reactions that will not react with iron. It is also important to wash the spatula after every use and to dry it well to prevent corrosion.

Conclusion

The main goal of the procedure was achieved without major complication.



 

Aspirin Hydrolysis.

Acetylsalicylic acid hydrolysis

In this experiment we will make salicylic acid

Salicylic acid's formula is C₆H₄(OH)COOH and its IUPAC name is 2-hydroxybenzoic acid. It finds use today ( among others ) as the active metabolite of acetylsalicylic acid (ASA), an acne treatment (a chemical exfoliant) and as a chemical reagent.In this experiment we will hydrolyse acetylsalicylic acid to salicylic acid (SA) with hydrochloric acid and reflux. Here is a look at the reaction scheme

One mole of ASA is hydrolysed to form one mole of SA and acetic acid (vinegar). Esters are generally formed through a condensation reaction called "Fischer-Speier esterification" where a carboxylic acid  is refluxed with an alcohol (usually in excess) to form an ester and a water molecule. this reaction requires an acid catalyst, which is usually concentrated sulphuric acid as it is a strong acid with dehydrating properties which drives the reaction to the right ( small amounts of the ester will be hydrolysed in water as the reaction is reversible) Although ASA is formed in a different way it  is technically an ester. This reaction is in essence the reverse where  water and dilute acid yield an acid and an alcohol ( but this reaction forms two acids ) 

Safety and Disposal: 

Before attempting any experiment be sure to read all relevant safety information on the chemicals you will be handling/producing. In this experiment it is highly recommended to wear gloves, wear eye protection, wear a lab coat and work in a well ventilated area (preferably out side or in fume hood). Concentrated Hydrochloric acid is highly corrosive along with its fumes. Strong fumes of acetic acid may be present in the flask after reflux. Salicylic acid can cause chemical burns. All of the acids used can burn and blind you and thus you must be prepared for such a situation if it would occur. Be sure to read all relevant disposal regulations, as it different depending on where you live the and author can't give such information. The author of this blog will not be held responsible for any damage caused by following directly or indirectly instructions/ gaining information from this blog. 

http://www.sciencelab.com/msds.php?msdsId=9924285

http://www.sciencelab.com/msds.php?msdsId=9927249

http://www.sciencelab.com/msds.php?msdsId=9922977

Procedure:

1. As always, time for some maths. first is calculation of theoretical yield: 

As seen from the reaction scheme the reaction is a 1:1 molar ratio, that is to say 1 mole of ASA hydrolyses to form 1 mole of SA. that makes calculations easy!

M= molar mass 

m= mass of sample

n= number of moles

From the formula n= m/M we can determine how much our theoretical yield will be from our sample

M(ASA)= 180.157 g/mol

the author's sample weighed 2.230 grams

From the formula n=m/M

n(ASA)=(2.230)/(180.157)

n= 0.0123 mol

if we rearrange the formula n=m/M we can determine the theoretical yield;

 m= nM 

M(SA)=138.121 g/mol

m(SA)= 0.0123x138.121

m(SA)= 1.706 g 

So there we have it, with a few simple calculations we can determine how much SA we get from this reaction.

     2. place 2.230 g of ASA into a 100 ml round bottom flask 

                   3. measure out in 50 ml graduated cylinder 1 ml of  >28 % w/w HCl and add 35 ml of distilled or deionised water. add this solution to the round bottom flask. add a few boiling chips to promote smooth boiling.

4. Clamp the flask just above a hotplate ( ensuring that the bottom of the flask is not directly touching the hotplate)

5. Attach a condenser and set up for reflux ( ensuring that the cold water is flowing from the bottom of the condenser up) reflux for 30-45 minutes 

6. Once refluxed the flask is stoppered and allowed to cool down to room temperature (make sure that the stopper is heavily greased) The SA is quite soluble at higher temperatures 

after about 15 minutes the SA precipitates due to its low solubility at room temperature (2g/L 20°C)

7. The product was vacuum filtered on a glass frit and was washed with 3x 30 ml ice cold distilled water ( probably over kill). The product was dried by drawing air over the product until it no more liquid was coming off and it was a free flowing powder.

              the final product was weighed and found to weigh 1.635 g representing a 95 % yield!

                                                        Notes:
 No melting point was taken ( as the author does not have the apparatus)  but it is highly recommended . The product may be re-crystalised  from acetone. Make sure your apparatus has no iron contaminants as it will produce a pink complex and will ruin your product.

                                                     References: 

http://www.chemguide.co.uk/physical/catalysis/hydrolyse.html

http://www.chemguide.co.uk/organicprops/alcohols/esterification.html

http://www.rsc.org/learn-chemistry/content/filerepository/CMP/00/000/045/Aspirin.pdf

Aspirin extraction.

Acetylsalicylic Acid extraction from Aspirin.

In this experiment, we will extract acetylsalicylic acid.
Acetylsalicylic acid, the major component of Aspirin tablets (the rest being inherit binders etc) is a useful laboratory reagent that can be used a starting point for organic synthesis. Acetylsalicylic acid (ASA) may be hydrolysed to salicylic acid with reflux and an acid catalyst. Aspirin, a cheap, common painkiller can be had cheaply at local supermarkets, this box will be the source of (ASA) for this extraction experiment. This ASA will be used in future experiments including hydrolysis, esterification ( methyl salicylate) and many other experiments.

                                                          Safety and disposal:
Before attempting any experiment be sure to read all relevant safety information on the chemicals you will be handling/producing. In this experiment it is highly recommended to wear gloves, wear eye protection, wear a lab coat and work in a well ventilated area. Keep an appropriate fire extinguisher handy as isopropanol is highly flammable. Be sure to read all relevant disposal regulations, as it different depending on where you live the author can't give such information. The author of this blog will not be held responsible for any damage caused by following directly or indirectly instructions/ gaining information from this blog.
http://www.sciencelab.com/msds.php?msdsId=9922977
http://www.sciencelab.com/msds.php?msdsId=9924412

                                                                          Procedure:

1. Firstly calculate the theoretical yield; The amount of tablets x the amount of ASA in each tablet.
 Chill in a freezer about 300 ml distilled or de-ionised water.

  

 This packet contains 7.2 g of
acetylsalicylic acid, the
maximum theoretical yield
of this extraction procedure;
24 tablets x 0.300 mg = 7.2 g

2. Measure about 1 ml of isopropanol per tablet (24 mL in my case) and add both aspirin and isopropanol in an appropriately sized Erlenmeyer flask.  

3.  Put some aluminium foil over the mouth of the flask and push through a thermometer until it is submerged by the isopropanol. Reflux the Erlenmeyer flask until all tablets are dissolved and broken down. Keep the temperature between 60-70° C (to minimise hydrolysis).

4. Once all tablets are broken down filter the solution and rinse the flask with a couple ml of isopropanol to quantitatively transfer all of the solution to the filter paper. Rinse the filter paper with a few ml of isopropanol and discard (ensure proper disposal).

5. To the filtered solution add 5x the amount of the solution in ice cold distilled or de-ionised water. this will precipitate the ASA from the solution as it is not highly soluble in  cold water-alcohol mixtures (more water than alcohol).
vacuum filter the precipitated ASA and wash with 3x 10 ml ice cold distilled or de-ionised water. Draw air over the product until dry and store in an appropriately labeled vial. weigh the product and calculate yield. Yield should be at least 80% with good lab technique.

 Additional notes
The product may be purified further with recrystallisation:
1. warm up about 50 ml of isopropanol
2. add ASA to beaker and then  add ( a little at a time) isopropanol until the aspirin dissolves and then filter.
3. allow isopropanol to evaporate at room temp the collect and store ASA. Done!
ASA hydrolyses at high temperatures and in with moisture so be sure to keep it in an air tight bottle!
                                                                                References
http://home.comcast.net/~drewpoche/CHEM3/CHEM_III_labs_files/Extraction%20of%20Acetyl%20Salicylic%20Acid.pdf
http://www.youtube.com/watch?v=xHg1hx7Rf64
http://www.sciencelab.com/msds.php?msdsId=9922977

Old Blog gone, here's my new one.

Hello everyone. My old blog was hacked/compromised/etc, so i can't upload experiments from it. Hence, i have created a new Blog.