Vanadium

Chemical reactions

Reaction of vanadium with acids


In a solution of acetic acid, sodium vanadate forms yellow decavanadate ions: [V10O28]6−, [V10O27(OH)]5−, [V10O22(OH)2]4−. The decavanadate ions exist at 1 > pH > 6.

VO43−(aq) + 25 H+(aq) [V10O27(OH)]5−(aq) + 12 H2O(l)

In mineral acids at pH ≥ 1, V(V) exist as the pale yellow dioxovanadium ions VO2+.

VO43−(aq) + 4 H+(aq) VO2+(aq) + 2 H2O(l)

In cold concentrated hydrochloric acid, red brown chloro complexes are formed.

V(V) is reduced to V(IV) by ascorbic acid. The reaction is fast [3].


Reaction of vanadium with air


Vanadium metal reacts with excess oxygen, O2, upon heating to form vanadium(V) oxide, V2O5. When prepared in this way, V2O5 is sometimes contamined by other vanadium oxides.

4V(s) + 5 O2(g) 2 V2O5(s) [yellow-orange]


Reaction of vanadium with bases


Vanadium metal is resistant to attack by molten alkali.

In strong alkaline solutions (pH > 13) V(V) exist as colorless orthovanadate ions, VO43−. At lower pH a protonized form is formed VO4(OH)2−, that condensates to pyrovanadate ions (12 > pH >9) [V2O7]4−, [HV2O7]3−, [V2O6(OH)]3−, and metavanadate ions (9 > pH > 6) [VO(OH)3], [VO2(OH)2]−, [V3O9]3−, [V4O12]4−.


Reaction of vanadium with ethanolamines


V(V) is reduced to V(IV) by amines [3].

Ethanolamines Reductive coefficient (x 10-6 M-1·s-1)
Monoethanol amine
Diethanol amine
Triethanol amine		 0.57
1.90
5.01
Reductive coefficients for ethanolamines adapted from [3].



Reaction of vanadium with glycols


V(V) is reduced to V(IV) by glycols [3].

Glycols Reductive coefficient (x 10-6 M-1·s-1)
Ethylene glycol
Diethylene glycol
Triethylene glycol
Tetraethylene glycol
PEG		 119
3.90
4.58
4.38
5.82
Reductive coefficients for glycols adapted from [3].



Reaction of vanadium with halogens


Vanadium reacts with fluorine, F2, when heated, forming form vanadium(V) fluoride

2 V(s) + 5 F2(g) 2 VF5(l) [colourless]


Reaction of vanadium with hydrogen peroxide


Alkaline solution:

VO43−(aq) + HO2−(aq) [V(O2)O3]3−(aq) [monoperoxovanadate, light yellow] + OH−(aq)

Acidic solution:

VO2+(aq) + H2O2(aq) V(O2)O+(aq) [monoperoxooxovanadium ions, red brown] + H2O(l)

In strong acidic solutions the V(O2)O+ ion is parted forming oxovanadium ions, VO2+

V(O2)O+(aq) + 2 H+(aq) VO2+(aq) [oxovanadium ions, blue] + O2(g) + H2O2(aq)


Reaction of vanadium with monosaccharides


V(V) is reduced to V(IV) by saccharides under acidic conditions [3].

Monosaccharide Reductive coefficient (x 10-5 M-1·s-1)
Hexoses D-fructose
D-galactose
D-glucose		 321
4.72
3.08
Pentoses D-ribose
D-xylose		 19.1
14.0
Reductive coefficients for saccharides and derivatives adapted from [3].



Reaction of vanadium with nucleotides


V(V) is reduced to V(IV) by L-cysteine. Reductive coefficient = 1.08·10-1 M-1·s-1 [3].


Reaction of vanadium with sulfide


V(V) is not precipitates by sulfide in 0.4M HCl, but is reduced to V(IV). Under alkaline conditions:

VO43−(aq) + 4 S2−(aq) + 4 H2O(l) VS43−(aq) [thiovanadate ions, red] + 8 OH−(aq)
VS43−(aq) + 6 H+(aq) V2S5(s) [black/brown] + 3 H2S(aq)


Reaction of vanadium with water


Vanadium does not reacts with water, under normal conditions.


Redox reactions of vanadium


V(V) is reduced under acidic conditions to the blue V(IV) (vanadyle ions) by reducing agents like H2S and SO2

VO2+(aq) + SO2(aq) VO2+(aq) + SO42−(aq)
VO2+(aq) + 2 OH−(aq) VO(OH)2(s) [brown]

Using strong reduction agents like Zn under acidic conditions reduces V(V) to V(II). During the transition, V(IV) [blue], and V(III) [green] can be observed.

2 VO2+(aq) + 3 Zn(s) + 8 H+(aq) 2 V2+(aq) + 3 Zn2+(aq) + 4 H2O(l)


Quantitative analysis


Method 3500-V C Inductively Coupled Plasma Method [1]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.005 mg/L
Method limit of detection in soil = 1.00 mg/kg