Aluminium tributanolate

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

other: review

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Conclusions:

the aluminium alkoxides are expected to hydrolyse rapdly

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

January 2018

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

no guideline followed

Principles of method if other than guideline:

test performed most likely at neutral pH only

GLP compliance:

no

Remarks:

Information on GLP is not reported. Quality of the report implies that GLP conditions were met.

Analytical monitoring:

yes

Buffers:

tested in water

Details on test conditions:

0.009 mol of aluminium tributanolate was added to 5.345 mol water (initial concentration 22.8 g/L) under continuous stirring. The resulting solution was hazy white. After further vigorously stirring for 4 hours, the solution was filtered to remove insoluble (aluminium compounds) and a sample of the resulting solution was analysed by gas-chromatography (no details available) for 1-butanol.

Duration:

4 h

pH:

7

Initial conc. measured:

22.8 g/L

Remarks:

concentration calculated, most likely tested at room temperature

Preliminary study:

No preliminary study was performed.

Test performance:

The design of the test was different from a standard hydrolysis study according OECD 111 (see above)

Transformation products:

yes

No.:

#1

Details on hydrolysis and appearance of transformation product(s):

the hydrolysis products are aluminium (III) species: hydroxide, hydroxyl oxide and oxide
In the water phase these species are formed by reaction of aluminium (III) species with water over time.

Al3+ + H2O --> Al(OH)3 --> Al(OH)O --> Al2O3

% Recovery:

> 90

Duration:

4 h

Remarks on result:

other: no details

DT50:

<= 4 h

Type:

not specified

Details on results:

The analyses showed that 1-butanol was present at 2.1%, which confirms almost complete hydrolysis. Temperature measurements did not show an increase in temperature of the initial solution during the stirring time, which would have been expected for the exothermic hydrolysis reaction. It seems, however, that the exothermic effect at the low concentration tested has been minimal.
No information on pH changes during the reaction is available, but in a similar test with the structural analogue alumium tri-isopropanol a clear but slight increase in pH was seen (initial pH 7 after 5 hours pH 8.75). It is shown that at this pH the aluminium species present are mainly Al(OH)4-, Al(OH)3 and Al(OH)2+ (see Langmuir et al. 2004, Issue paper on the environmental chemistry of metals, US EPA Contract #68 -C-02 -060). The identity of aluminium3+ species was not determined in the experiment with aluminium tributanolate or in the experiment with aluminium tri-isopropanolate.

Conclusions:

the substance hydrolyses completely under the conditions of the test

Description of key information

For the aluminum alkoxides, there is a two-step process of degradation. The first step is the hydrolysis of the aluminum alkoxides to their constituent linear alcohols and alumina.  

The reaction mechanism is described in depth in Brinker and Scherer (1990), who indicate that under neutral, acid or base conditions it is expected that the hydrolysis and condensation reactions would be quite rapid. While no rates of hydrolysis for aluminum alkoxides are available in the literature, data for silicone alkoxide show rapid hydrolysis (log Kspont) in aqueous systems. Log Kspont values within the pH range 4 to 10 vary from approximately -4 at neutral pH to -2 at both acid and base pH. Since this reaction is acid catalyzed, the rate at pH 1 is anticipated to extend even further upward from the "acidic portion" of the curve. 

Based on reaction dynamics, aluminum alkoxide would be expected to be even faster than silicone alkoxide under both environmental and physiological conditions (Brinker and Scherer 1990).

Under neutral conditions, it is expected that both hydrolysis and condensation of aluminium alkoxides occur by nucleophilic addition, followed by proton transfer and elimination of either water or alcohol in a manner analogous to transition metal alkoxides. Likewise, both of these reactions are catalyzed by addition of either acid or base. Acids protonate OR or OH ligands creating good leaving groups and eliminating the requirements for proton transfer in the intermediate. Bases deprotonate water or OH ligands, creating strong nucleophiles. (Brinker and Scherer 1990).

The findings as described above are also observed in a limited reported hydrolysis study on aluminium tributanolate.

0.009 mol of aluminium tributanolate was added to 5.345 mol water (initial concentration 22.8 g/L) under continuous stirring. The resulting solution was hazy white. After further vigorously stirring for 4 hours, the solution was filtered to remove insoluble (aluminium compounds) and a sample of the resulting solution was analysed by gas-chromatography (no details available) for 1-butanol. The analyses showed that 1-butanol was present at 2.1%, which confirms almost complete hydrolysis. Temperature measurements did not show an increase in temperature of the initial solution during the stirring time, which would have been expected for the exothermic hydrolysis reaction. It seems, however, that the exothermic effect at the low concentration tested has been minimal.
No information on pH changes during the reaction is available, but in a similar test with the structural analogue aluminium tri-isopropanol (Sasol 2000) a clear but slight increase in pH was seen (initial pH 7 after 5 hours pH 8.75). It is shown that at this pH the aluminium species present are mainly Al(OH)₄^-, Al(OH)₃and Al(OH)²⁺(see Langmuir et al. 2004, Issue paper on the environmental chemistry of metals, US EPA Contract #68 -C-02 -060). The identity of aluminium³⁺species was not determined in the experiment with aluminium tributanolate or in the experiment with aluminium tri-isopropanolate.

Key value for chemical safety assessment

Half-life for hydrolysis:

4 h