Reaction products of disubstituted alkane, nickel, (Z/E)-substituted alkene, reaction mass of tetraalkyl-3,3’-di(propan-2-yl)-biphenyl-diyl tetrakis(dialkylphenyl) bis(phosphite) and tris(dialkylphenyl) phosphite and zinc halide

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Qualifier:

no guideline followed

Principles of method if other than guideline:

The test item saturated with water (2-phase system) was stirred and incubated under aerobic conditions. The kinetics of disintegration of the Ni-charge-transfer complex was investigated by monitoring a) organic ligand displacement followed by (31)P-NMR; b) disappearance of active nickel in catalyst solution followed by HPLC; c) appearance of phosphite oxidation products followed by (31)P-NMR.

Radiolabelling:

no

Remarks on result:

not determinable because of methodological limitations

Remarks:

Analysis of recovery including mass balancing was not possible due to several molecular species present in the original test item (UVCB), the rapid hydrolytic / oxidative decomposition of Step 2 catalyst and the multitude of species resulting therefrom. Analytical methods are however very well developed and appropriate for this study (see details in section 1.4 IUCLID: Analysis_Identification_CBI v8.pdf; Analysis_Quantification_CBI v8.pdf.

Key result

pH:

7

Temp.:

35 °C

Hydrolysis rate constant:

0.019 min-1

DT50:

35.7 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Derived from disappearance of active nickel in catalyst solution (i.e. Step 2 catalyst) followed by HPLC, and confirmed by results from disappearance of Step 2 catalyst followed by (32)P-NMR.

Other kinetic parameters:

Appearance of phosphite oxidation products in catalyst solution followed by (31)P-NMR: the same pseudo-first order rate constant applies to this parameter (0.0194/min) as derived from disappearance of Step 2 complex from catalyst solution followed by HPLC (quantifying active Ni) and confirmed by results from disappearance of Step 2 catalyst followed by (32)P-NMR.

Details on results:

See IUCLID section "Any other information on results incl. tables" below.

Throughout the experiment conversion of Step 2 catalyst to hydrolysis products, 2,4-xylenol, and oxidation products was monitored by 31P-NMR (hydrolysis and oxidation products) and GC (2,4-xylenol). A table of abbreviations, molecular structures, and CAS numbers (as far as available) of the phosphite compounds initially present as well as identified transformation products which are relevant to this investigation is attached under IUCLID section "attached background material".

Progressive disappearance of Step 2 catalyst and all phosphites was observed as soon as the experiment began. Conversion of the free (i.e. not part of actual Step 2 catalyst) phosphites (D80, T80, and C80) is primarily to hydrolysis products initially (LHP-D2, LHP-T2, and LHP-B). Conversion of the D80 ligand of Step 2 catalyst (complexed with active Ni) is essentially exclusively to oxidation products (D80-O and D80-O2) under the conditions of this investigation.

Hydrolysis products of the phosphite ligands in the sample were observed to increase from approximately 2% of the total phosphorous in the sample by 31P NMR (before addition of water) to ~5.5% during the experiment. Oxidation products of the phosphites in the samples were observed to increase significantly over the course of the investigation, from initially 18.2% to ca. 50% after one hour. At later time points, no further increase could be determined by NMR (see Figure 2).

Over the course of the experiment the concentration of active nickel in the sample was monitored by HPLC and was observed to decrease from an initial concentration of 2670 ppm to 57 ppm after 3.3 hours, and to be below the detection limit (1 ppm) by 6 hours.

The rate of Step 2 catalyst disappearance was determined to be approximately 0.4%/minute by both following the disappearance of coordinated D80 (by 31P NMR; see Figure 1), and disappearance of active nickel (by HPLC) in the sample (see Figure 2). A pseudo first-order rate constant of 0.0194/min was derived from disappearance of active nickel in catalyst solution (i.e. Step 2 catalyst) followed by HPLC, and confirmed by results from disappearance of Step 2 catalyst followed by (32)P-NMR. Kinetics of appearance of phosphite oxidation products in catalyst solution followed by (31)P-NMR was observed to be characterized by the same pseudo-first order rate constant (0.0194/min) as derived from disappearance of Step 2 complex from catalyst solution, as becomes obvious from the following results tables:

Based on Figure 2: Disappearance of active nickel in catalyst solution followed by HPLC

Time [min]	ppm Ni	k	ppm Ni, calculated with k [/min] =	0.0194
0	2670
198	57	0.01943	57.00
360	0.5*	0.02384	2.45
				corresponding half-life: 35.7 min

*) below limit of detection: 1/2 of the limit value was set for this time point. Because of this, calculation of rate constant k from this value is associated with higher uncertainty.

Analysis according to first order kinetics: ln[A] = ln[A0] –kt; k= (ln[A0] - ln[A])/t

Based on Fig. 1: Disappearance of Step 2 catalyst followed by (32)P NMR

Time [min]	% 31P	%31P, calculated with k [/min] =	0.0194
0	25.4	25.40
15	19	18.98
30	19.3	14.18
45	12.1	10.60
60	0.8	7.92
90	0.7	4.42
150	0.6	1.38
210	0	0.43

Based on Fig. 3: Appearance of phosphite oxidation products in catalyst solution followed by (31)P NMR

Time [min]	% 31P		% 31P calculated with K [/min] =	0.0194
0	18.2		18.20
15	28.9		24.36
30	31.3		32.60
45	39.9		43.63
60	48.4	47.6*	58.39
90	46.1
150	47
210	48.8

*)Arithmetic mean for 60, 90, 150, and 210 min

As a conclusion, degradation of Step 2 catalyst under aerobic conditions in water by hydrolysis and oxidation is rapid: in the water-saturated organic system applied in this study, after 4 hours essentially no Step 2 catalyst was left based on both, active nickel as well as quantification of phosphites by (32)P NMR. This rapid decline is chronologically fully in line (same rate constant) with the increase of phosphite oxidation products determined by (31)P NMR.

Throughout the experiment the medium was observed to become “milky” and as the reaction progressed it was evident that a precipitate was forming.  This solid, which was pale green in colour, was isolated and analyzed by ICP and FTIR after the reaction, and was found to be soluble in acid and basic media. It was identified as nickel(II) hydroxide. The FTIR spectrum of the solids obtained from the experiment had a lack of any peaks indicative for phosphites present in Step 2 catalyst solution. This further supports nickel release from the ligand and is consistent with Ni(OH)2. Visually, Step 2 catalyst solution changed during the study from a dark red to a milky yellow with a thick layer of precipitate (Ni(OH)2) on the bottom.

After degradation of Step 2 catalyst the remaining phosphites and phosphates will continue to react quickly to afford aryl alcohols, phosphorous and phosphoric acids via known pathways (detailed analysis by Garner, 2003). The final aromatic reaction products resulting from phosphites initially present in Step 2 catalyst solution will therefore be LHP-fin1 (2,4-xylenol, CAS 105-67-9 ) and LHP-fin2 (5,5',6,6'-tetramethyl-3,3'-bis(propan-2-yl)-[1,1'-biphenyl]-2,2'-diol; no CAS No. available) as well as phosphoric and phosphorous acid, in the following approximate molar ratios:

LHP-fin1 : LHP-fin2 : phosphoric and phosphorous acid = 4 : 1 : 2.

References:

NIS-2003-E-41, Degradation pathways, competitive kinetic studies, and models for the gen 4 ligand and catalyst; J. Michael Garner.

Validity criteria fulfilled:

not applicable

Remarks:

This study was performed for another regulatory purpose and thus differs compared to studies on hydrolysis as a function of pH.

Reference 2

Endpoint:

hydrolysis

Data waiving:

other justification

Justification for data waiving:

the study does not need to be conducted because the substance is readily biodegradable

Description of key information

No hydrolysis test is required for the submission substance due to its ready biodegradability (waiving according to 'Column 2' of REACH Annex VIII).

Based on a reliable supporting study, the following key information was derived:

Pseudo-first order rate constant for decomposition of Step 2 catalyst by hydrolysis / oxidation at 35 °C (pH 7):

k= 0.0194 /min; corresponding half-life: 35.7 min.

Final products of hydrolysis/oxidation:

LHP-fin1 (dialkylphenol); LHP-fin2 (hexaalkyl-biphenyl-diol); phosphoric and phosphorous acid, in molar ratios:

4 : 1 : 2

Key value for chemical safety assessment

Half-life for hydrolysis:

35.7 min

at the temperature of:

35 °C

Additional information

This reliable and scientifically valid study was performed for another regulatory purpose and thus differs compared to studies on hydrolysis as a function of pH. The objective of the study was to determine the (abiotic) fate of Step 2 catalyst in case of an accidental chemical spill in the aqueous aerobic environment. In the focus of the study is the stability of Step 2 catalyst as well as hydrolysis of the insoluble aromatic phosphite compounds (mainly ligand D80). Other compounds present in Step 2 catalyst solution ((Z/E)-substituted alkene, disubstituted alkane) are known to be of relatively high water solubility, stable to hydrolysis and readily biodegradable, and were therefore not assessed in this study. Results give valuable insight in routes and kinetics of decomposition and transformation of Step 2 catalyst.

The test item saturated with water (2-phase system) was stirred and incubated under aerobic conditions at 35 °C (pH 7) over a period of 6 hours (total incubation phase). The kinetics of disintegration of the transition metal-charge-transfer complex was investigated by monitoring a) organic ligand displacement followed by (31)P-NMR; b) disappearance of active transition metal in catalyst solution followed by HPLC; c) appearance of phosphite oxidation products followed by (31)P-NMR. Molecular structures of relevant hydrolysis and oxidation products were identified.

Kinetics observed for all three parameters were in line with pseudo-first order kinetics, with a first order rate constant of k= 0.0194 /min and a corresponding half-life of 35.7 min.

Throughout the experiment the medium was observed to become “milky” and as the reaction progressed it was evident that a precipitate was forming. This solid, which was pale green in colour, was isolated and analyzed by ICP and FTIR after the reaction, and was found to be soluble in acid and basic media. It was identified as transition metal hydroxide. The FTIR spectrum of the solids obtained from the experiment had a lack of any peaks indicative for phosphites present in Step 2 catalyst solution. This further supports transition metal release from the ligand and is consistent with transition metal hydroxide. Visually, Step 2 catalyst solution changed during the study from a dark red to a milky yellow with a thick layer of precipitate (transition metal hydroxide) on the bottom.

After degradation of Step 2 catalyst the remaining phosphites and phosphates will continue to react quickly to afford aryl alcohols, phosphorous and phosphoric acids via known pathways (detailed analysis by Garner, 2003). Rapid hydrolytic degradation of phosphites to aryl alcohols, phosphoric and phosporous acid is inherent to the nature of these compounds and well known, e.g. for triphenylphosphite (CAS 101 -02 -0). The final aromatic reaction products resulting from phosphites initially present in Step 2 catalyst solution will therefore be LHP-fin1 (dialkylphenol) and LHP-fin2 (hexaalkyl-biphenyl-diol)) as well as phosphoric and phosphorous acid, in the following approximate molar ratios:

LHP-fin1 : LHP-fin2 : phosphoric and phosphorous acid = 4 : 1 : 2.