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LUBRIZOL TEST PROCEDURE
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TP-AATM-111C-02Edition: October 17, 2006
Previous Edit ion: May 29, 2000
Hydroxyl Value (Hindered Hydroxyls)DEFINITION
This method determines the number of hydroxylgroups present
which can be acetylated under theconditions of this test. It is
useful for determininghindered (secondary or tertiary) hydroxyl
groupswhich are not acetylated in the pyridine - aceticanhydride
system described in Lubrizol TestProcedure TP-AATM-111A-02.
Hydroxyl valueis defined as the number of milligramsof potassium
hydroxide necessary to neutralize theacetic acid which combines on
the acetylation of onegram of sample.
DESCRIPTION OF METHOD
A specified weight of sample is acetylated by heatingat 70-72C
for one hour with a measured amount ofacetic anhydride in an ethyl
acetate solution which
contains p-toluenesulfonic acid as catalyst. Thehydroxyl groups
react with the acetic anhydride toform the acetate and free acetic
acid. At the end of thereaction period, all the unconsumed acetic
anhydrideis hydrolyzed to free acetic acid by the addition ofwater
(and pyridine), and heated for ten minutes toinsure complete
hydrolysis. The sample and acorresponding reagent blank which has
been run atthe same time are titrated with 0.5N methanolicpotassium
hydroxide. A mixed indicator consisting ofcresol red and thymol
blue is used for the titration.
The difference between the blank and the sampletitrations
represents the amount of acetic acidconsumed by the sample. The
hydroxyl value iscalculated (by definition) as the
equivalentmilligrams of potassium hydroxide per gram ofsample. The
amount of potassium hydroxideconsumed by the free acids present in
the samplemust be included in the calculations.
Excess acetic anhydride is required to drive thereaction to
completion. Therefore, special attentionmust be paid to the ratio
of sample size to reagentas set forth in the table shown in the
procedure.
APPARATUS
1. 250 ml ground neck erlenmeyer flasks, TS24/40, with air
condenser.
2. Controlled oil bath regulated to maintain thetemperature at
70-72C.
3. Cooling bath. ( Shallow water-filled pan).4. Class A
volumetric pipette calibrated to deliver
5 (0.03) ml or appropriate dispenser.
5. Analytical balance capable of weighing to thenearest 0.1
mg.
6. Burette (50 ml) Class A with a tolerance of0.05 ml.
7. Assorted Mohr pipettes, graduated cylinders,droppers.
8. Magnetic stirrer, stirring bars.
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Lubrizol Test Procedure TP-AATM-111C-02Hydroxyl Value (Hindered
Hydroxyls)
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REAGENTS AND SOLUTIONS
1. Acetic Anhydride Reagent - 60ml acetic anhy-dride, 7.2g
p-toluenesulfonic acid and 180ml ethylacetate.
2. Pyridine-water solution - approximately 3mlpyridine for each
1ml water.
3. Cresol Red-Thymol Blue Indicator Solution - 1 partCresol Red
(0.1% in H2O)+3 parts Thymol Blue(0.1% in ethanol).
4. Methanolic potassium hydroxide 0.5N -commercially
available.
PROCEDURE
It is recommended that all blanks and sample be runin
duplicate.
1. Accurately weigh the specified amount of sampleinto a 100 ml
acetylation flask according to thefollowing table and record weight
to the nearest0.1 mg.
Hydroxyl value Sample Size0-20 5.0g (0.1)20-100 2.0g
(0.1)100-150 1.5g (0.1)150-200 1.0g (0.05)200-250 0.75g (0.05)
2. Into each flask, accurately add 5 ml of aceticanhydride
reagent and attach an air condenser. Atthe same time set up reagent
blanks, containingno sample but the corresponding volume
ofreagent.
3. Place the flasks in the 70-72C oil bath, immersingto the
liquid level. Swirl vigorously until all thesolid material is
melted and is thoroughly mixedinto the solution.
4. Continue heating at 70-72C for one hour, swirling
the flasks frequently to insure uniform reaction.5. Remove the
flasks from the oil bath and cool for at
least ten minutes in a room temperature shallowwater bath.
6. To each flask through the air condenser, using aMohr pipette,
add 2 ml of deionized water.
7. Using a Mohr pipette, add 10 ml of pyridine-watersolution
(reagent) to each flask through the aircondenser.
8. Swirl vigorously to mix thoroughly. Return theflasks to the
oil bath for 10 minutes to completethe hydrolysis of the excess
acetic anhydridereagent. Swirl at frequent intervals.
9. Remove the flasks from the oil bath and placethem in the
cooling bath for at least tenminutes.
10. Remove the condenser. Using a dropper, add1 ml of the
indicator solution. Add a magneticstirring bar.
11. Fill burette and titrate the blanks and thesamples using 0.5
N methanolic potassiumhydroxide.
NOTE: The end point color of the blank is abold blue color with
no trace of red whenviewed against the light.
The end point color of the sample will vary tosome extent
depending upon the color ofthe test sample. The final color is
usually adeep gray blue with the disappearance ofthe last traces of
red color marking the endpoint. The sample should be heated
underhot water to release any remaining occludedtraces of acid just
before the end of thetitration.
An alternate method may be used by adding(by pipette) 10 ml
pyridine to each flask justbefore titration. This is found to be
preferableby some analysts who feel that it improves thesharpness
of the end point. Either method oftitration may be used only if all
samples andblanks receive identical treatment.
12. Read the burette to two decimal places andrecord the mls
used by all samples and blanks.
13. Determine the acid value of the sample (AATM109).
