Oxidation of alcohol in beer

[alhc]

Hi, i've read the other posts on the oxdiation of alcohols in wine and i find it very interesting, however contrary to his experiment im attempting to design and conduct an experiment whereby i find out the rate of oxidation of alcohol in beer. It is known that the oxidation of alcohol in beer (if i leave it exposed to air) is mainly due to the bacteria that is working on it. I do not know how long i should hold this experiment and the way about to do it. If i use some Potassium dichromate or potassium permaganate to instantly titrate it to completely oxidise the solution and backtitrate with hydrogen peroxide ( for permaganate) or potassium iodide and sodium thiosulfate (for dichromate). The colour stands in the way, i have yet to try activated carbon though to see whether it is possible to remove any organic coluring within the solution, but my fear in doing so would be to remove the ethanol which im investigating into. So if anyone has any knowledge over this please do help i'm in serious need for some help

[DrDNA]

Hi, i've read the other posts on the oxdiation of alcohols in wine and i find it very interesting, however contrary to his experiment im attempting to design and conduct an experiment whereby i find out the rate of oxidation of alcohol in beer. It is known that the oxidation of alcohol in beer (if i leave it exposed to air) is mainly due to the bacteria that is working on it. I do not know how long i should hold this experiment and the way about to do it. If i use some Potassium dichromate or potassium permaganate to instantly titrate it to completely oxidise the solution and backtitrate with hydrogen peroxide ( for permaganate) or potassium iodide and sodium thiosulfate (for dichromate). The colour stands in the way, i have yet to try activated carbon though to see whether it is possible to remove any organic coluring within the solution, but my fear in doing so would be to remove the ethanol which im investigating into. So if anyone has any knowledge over this please do help i'm in serious need for some help

The ethanol should not absorb to the charcol.

Why don't you try out your experiment first with distilled water and pure ethanol? That will eleminate any variables.

 

 

Here are some neat things for you to try.......

Organic Reactions

Objectives

Synthesis of some important esters.

Oxidation of a primary alcohol first to an aldehyde and then a carboxylic acid.

To saponify a typical vegetable oil.

Grading

You will be assessed on

detailed answers required in the lab report.

the correctness and thoroughness of your observations.

Introduction

Esters are an important class of organic compounds commonly prepared from the esterification reaction of an organic acid with an alcohol in the presence of a strong mineral acid (usually H2SO4). They are chiefly responsible for the pleasant aromas associated with various fruits, and as such are used in perfumes and flavorings. Some esters also have useful physiological effects. The best known example is the analgesic ("pain killing") and anti-pyretic ("fever reducing") drug acetylsalicylic acid, otherwise known by its trade name aspirin.

Liniments used for topical relief of sore muscles contain the ester methyl salicylate ("oil of wintergreen"), which is prepared from the reaction of methyl alcohol with the acid group of salicylic acid. Methyl salicylate acts as an analgesic and is absorbed through the skin; however, methyl salicylate is also a skin irritant (like many organic substances), which in this instance provides the beneficial side effect of the sensation of warming in the area of the skin where the liniment is applied.

Oxidation of a primary alcohol may yield either an aldehyde or a carboxylic acid, depending on the reaction conditions. For example, mild oxidation of ethanol produces acetaldehyde, which under more vigorous conditions may be further oxidised to acetic acid. The oxidation of ethanol to acetic acid is responsible for causing wine to turn sour, producing vinegar.

A number of oxidising agents may be used. Acidified sodium dichromate (VI) solution at room temperature will oxidise primary alcohols to aldehydes and secondary alcohols to ketones. At higher temperatures primary alcohols are oxides further to acids.

 

Figure 1

 

 

The dichromate solution turns from the orange color of the Cr2O72− (aq) to the blue color of the Cr3+ (aq). This color change is the basis for the "breathalyser test". The police can ask a motorist to exhale through a tube containing some orange crystals. If the crystals turn blue, it shows that the breath contains a considerable amount of ethanol vapor.

Soaps are produced by the reaction of metallic hydroxides with animal fats and vegetable oils. The major components of these fats and oils are triglycerides. Triglycerides are esters of the trihydroxy alcohol called glycerol and various long-chain fatty acids. Tristearin is a typical triglyceride. Upon reaction with sodium hydroxide, the ester bonds of tristearin are broken. The products of the reaction are the soap, sodium stearate, and glycerol. This type of reaction is called saponification (Greek: sapon, soap) and it is depicted below.

 

 

Figure 2

 

 

Soap is made commercially by heating beef tallow in large kettles with an excess of sodium hydroxide. When sodium chloride is added to this mixture (called the "saponified" mixture), the sodium salts of the fatty acids separate as a thick curd of crude soap. Glycerol is an important by-product of the reaction. It is recovered by evaporating the water layer. The crude soap is purified, and coloring agents and perfumes are added to meet market demands.

EXPERIMENTAL PROCEDURE

CAUTION WEAR EYE PROTECTION!

 

CAUTION - Concentrated sulfuric acid will burn and stain the skin as well as damage clothing. In case of skin or clothing contact, wash the area immediately with large amounts of water.

Synthesis of esters

Place approximately 2 g (or 2 mL if the substance is a liquid) of the organic acid and 2 mL of the alcohol in a large test tube.

Add 5 - 7 drops of concentrated (18 M) sulfuric acid, mix the solution well with a glass stirring rod and then place the test tube in a hot water bath (largest beaker in your drawer) (~ 80°C) for 5 - 10 minutes.

Remove the test tube from the hot water bath and cautiously pour the mixture into about 15 mL of saturated sodium bicarbonate contained in a small beaker. The sodium bicarbonate will destroy any unreacted acid.

Observe the aroma produced from each of the following esterification reactions. Write the structure of the esters produced, and the balanced equations for the esterification and the acid/sodium bicarbonate reactions:

 

Complete the following reactions using the procedure above and record your observations.

 

(1) C7H6O3+CH3OH→

salicylic acid + methyl alcohol

(2) CH3CH2CH

2

CH2CH2CH2CH2CH2OH+CH3COOH→

1 - octanol + glacial acetic acid

(3) CH3CH2CH

2

CH2CH2OH+CH3COOH→

amyl alcohol + glacial acetic acid

(4) C2H

5

OH+CH3COOH→

ethanol + acetic acid

 

Oxidation of an alcohol with acidified potassium dichromate(VI) solution

Add 10 drops of dilute sulfuric acid (6M) and 5 drops of potassium dichromate(VI) solution (0.01M) to 5 drops of ethanol. The oxidising agent is added slowly to the alcohol so that the temperature is kept below that of the alcohol and above that of the carbonyl compound. (Carbonyl compounds are more volatile than the corresponding alcohols). Usually the alcohol is in excess of the oxidant and the aldehyde is distilled off to avoid further oxidation.

Note the color and smell cautiously (Royal Wave).

Warm the mixture and smell cautiously (Royal Wave).

Repeat the experiment using first methanol and then propan-2-ol in place of ethanol.

 

Describe what happens and explain the color changes.

What conditions and techniques would favour the oxidation of ethanol to

a. ethanal rather than ethanoic acid.

b. ethanoic acid rather than ethanal?

Oxidation of an alcohol with acidified potassium permanganate (VII) solution

Add 10 drops of dilute sulfuric acid and 5 drops of potassium permanganate (VII) solution (0.01M) to 5 drops of ethanol. Note the color and smell cautiously.

Warm the mixture and smell cautiously (Royal Wave).

Repeat the experiment using first methanol and then propan-2-ol in place of ethanol.

Take the pH of your final mixture using Universal indicator paper

Describe what happens and explain the color changes.

What is your final product?

Saponification of a vegetable oil

CAUTION - Sodium hydroxide is a very caustic material that can cause severe skin burns. Eye burns caused by sodium hydroxide are progressive: what at first appears to be a minor irritation can develop into a severe injury unless the chemical is completely flushed from the eye. If sodium hydroxide comes in contact with the eye, flush the eye with running water continuously for at least 20 minutes. Notify your TA immediately. If sodium hydroxide is spilled on some other parts of the body, flush the affected area with running water continuously for at least 2-3 minutes. Notify your TA immediately.

Never handle sodium hydroxide pellets with your fingers. Use weighing paper and a scoopula. Solid sodium hydroxide will absorb water from the atmosphere. It is hygroscopic. Do not leave the container of sodium hydroxide open.

Keep ethanol and ethanol-water mixtures away from open flames.

Aqueous iron chloride will stain clothes permanently and is irritating to the skin. Avoid contact with this material.

 

In this experiment, you will saponify a vegetable oil

Pour 5 mL (5.0 g) of vegetable oil into a 250-mL beaker.

Slowly dissolve 2.5 g of NaOH pellets in 15 mL of the 50% ethanol/water mixture in a 50-mL beaker.

Add 2-3 mL of the NaOH solution to the beaker containing the oil. Heat the mixture over a hot plate with stirring. CAUTION: Keep your face away from the beaker and work at arm's length. Stirring is required to prevent spattering. Every few minutes, for the next 20 minutes, add portions of the ethanol/water mixture while continuing to stir to prevent spattering. After about 10 more minutes of heating and stirring, the oil should be dissolved and a homogenous solution should be obtained.

Add 25 mL of water to the hot solution. Using the hot grips, pour this solution into a 250 mL beaker containing 150 mL of saturated NaCl solution. Stir this mixture gently and permit it to cool for a few minutes.

Skim the soap layer off the top of the solution and place it in a 50-mL beaker.

Into a test tube, place a pea-sized lump of your soap. Place a similar amount of laundry detergent in a second tube and a similar amount of laundry detergent in a second tube and a similar amount of hand soap in a third tube. Add 10 mL of water to each tube. Stopper each tube and shake thoroughly.

Estimate the pH of the solution using wide-range indicator solution or wide-range test paper. Record the results. Pour the contents of the test tubes into the sink and rinse the tubes with water.

http://cnx.org/content/m15483/latest/

 

A Breathalyzer is a device that is used to determine the amount of alcohol in an individual's blood stream. Individuals are asked to blow into a Breathalyzer. The exhaled alveolar air is used to determine the concentration of alcohol in the individual's blood stream. The ratio of breath-alcohol to blood-alcohol is 2,100:1. This means that 2,100 milliliters (ml) of alveolar air will contain the same amount of alcohol as 1 ml of blood. The device has a mouthpiece, a tube through which the individual exhales air, and a sample chamber where this air sample in analyzed. The breath sample is bubbled through a mixture of sulfuric acid, potassium dichromate, silver nitrate and water. The sulfuric acid removes the alcohol from the air sample and converts it into a liquid solution. Sulfuric acid also provides the acidic conditions necessary for the reaction to take place. Silver nitrate is a catalyst in this reaction and the dichromate ion is the reactant that undergoes a color change when it reacts with ethanol. The degree of color change is directly related to the amount of ethanol in the air sample. Dichromate reagents are a dark orange-red color and are chemically transformed into chromium III ions, which are green. Potassium permanganate is another reactant that is sometimes used. Permanganate ions are purple and turn colorless with the oxidation of ethanol. These color changes are the basis of the Breathalyzer.

[alhc]

Hmmm, okay here are some of the problems im facing at the moment with my experiment. I have no intentions of changing my topic so yea... I'm gonna stick to it and figure out how i'm actually going to get results!

 

First of all, i tried to find out the concentration of ethanol within beer by attempting to oxidise it using potassium maganate (but surely the sugars in beer will be reacting with it as well, i thought of just stating it in my error analysis), and back titrating with hydrogen peroxide to find out the amount of potassium maganate used so as to calculate the amount of ethanol present within beer. But when the reaction creates a brown sludge like substance which i cant work with as such i cant find out how to get the amount of ethanol present within beer. But i've found this website which shows how to get the amount of ethanol out from beer but now i need a quenching reagent which i cant seem to find. The site for this particular method is http://www.outreach.canterbury.ac.nz/chemistry/ethanol.shtml

 

Secondly, I think this is more successful, i've tested the P.H of the beer at the initial stages which is approx 4.78 or so (this is half and hour after it has been exposed to air) and the beer P.H after 24 hours is around 3.01. So i know that it is possible but tedious to find out the rate of production of acids within beer. The only problem that i'm facing is the titration, as i'm using relatively pure sodium hydroxide so as to compeltely react with the weak ethanoic acids and with phenolphthalein as an indicator, the only problem is the colour change, which might be a bit inaccurate as the colour change in beer is not that significant compared to a normal acid-base titration where the colour change is obvious.

 

As such if anyone has any advice on such a topic do help please any help is greatly appreciated!

 

Thanks Dr.DNA for your help it helped me think through certain things

[ecoli]

First of all, i tried to find out the concentration of ethanol within beer by attempting to oxidise it using potassium maganate (but surely the sugars in beer will be reacting with it as well, i thought of just stating it in my error analysis),

 

I don't know... isn't there a lot more carbohydrate in beer than ethanol?

 

There's about 13 grams of carbos in 350 ml of beer (from a google search). Most beer has 3-5% alcohol by mass.

[alhc]

Oooo... sorry my knowledge of chemistry is rather limited... i didnt know carbohydrates get oxidised too... sigh i guess the KMnO4 would be useless then... so i'm thinking of using the website i gave by evaporating the amount of ethanol in beer but for that to happen i guess i need to have a quenching reagent for it to stop at the allocated time.

[alhc]

Can someone answer my querie whether alcohols in beer under the influence of bacteria will oxidise to form aldehyde or will it fully oxidise to form ethanoic acid?

[fredrik]

In general that's a complex question. Certainly there are off products in most processes, and there are so many strains and speices of bacterias that it may vary. From the beer and wine fields it's known that a range of both bacterias as well as yeasts sometimes produces a mixtures of ethanol, organic acids as well as aldedhydes. But relatively speaking I think the acetaldehyde makes up a small part. It's often toxic even to the cell and puts additional stress on the cell.

 

To monitor pH and from that deduce acid production you also need to know the buffering system, which usually in itself contains many variables.

 

About measuing..

 

I don't know what you are doing if it's a hobby project or school project or what the purpose is but some ideas if you like playing I have tried a electronic gas sensor that is senitive to ethanol.

 

For example http://www.efo.ru/doc/Sencera/Sencera.pl?919 - this is a type that can be used in simple digital breathalyzers.

 

I have tried this, and by hooking it up with a basic circuit you easily build yourself I was able to achieve excellent resolution on the ethanol level in beer. I simply submerge this sensor in the headspace over a glass o beer - wait 5 minutes for equilibration and take a reading.

 

I tried several beers and the resolution was suggesting that it has potential. But the problem was to get a stable and reliable calibration, because temp changes in the beer as well as the electronics made huge drifts. So for a serious device you need to have temperature compensation probably + a stabilized electroic circuit. I think there was also an issue of self- heating of the sensor.

 

There are a lot of fun stuff you can do at home with only basic electronic skills, a simple A/D device for your PC and imagination.

 

Measurement errors can usually be compensated for by making mathematical error corrections but then that might be too complicated if you aren't into chemistry.

 

I think you should first determine the purpose and what resolution you want in your measurements. There are many more or less crude methods.

 

Brewers tend to use hydrometers to monitor the fermentation process, and I'm sure if you can expand this model to incorporate a pH reading, a typical buffering system with some assumptions to monitor also a mix of acetic acid. Then you can add som theoreitcal modelling yo our experiment and it will get alot more fun

 

Also wether you have alot of acetaldehyde you can simply try. Once you learn to identify the smells you can smell it. This compound has an extremely low treshold.

 

/Fredrik

[alhc]

Hmmm here's what actually happened in the labs today as i tried to find out the amount of acid present within beer initially...

 

I attempted using an indicator which totally blew it didnt work one bit and then i went on to using PH to find out the amount of acid that is present by titrating with a weak base. As the end point would be completely uncertain as it would be a basic ending ( titrating a weak acid [assuming acids in beer are all weak] with a strong base). I tried finding the PH curve to it but ended up more or less with a straight line and it's strange why there would be a linear line with a acid - base reaction PH curve...

[John Cuthber]

There are possibly a number of different acids of different strengths, each gives a small step in the pH curve but they get added together to form a more or less straight line.

[alhc]

That's what i thought as well... but if that's the case then it would be difficult for me to measure the rate in which the alcohol oxidises to form acid... then again i wouldnt know as to whether acids are actually formed or not... But i did test the ph after one day after exposiing it to air and it was approx 3.03 whereas the initial ph was around 4.77... so yea im trying to find out a way to find out the amount of acid...

[John Cuthber]

It won't win any prizes for accuracy, but you could measure the NaOH taken to titrate the pH back to 4.77 as a measure of the acid produced.

A better way would be to distill over the acetic acid- most of the other acids present won't be volatile, then titrate it.