Question

In Ziegler-Natta polymerization of ethylene, the active species is:
A. $AlC{l}_3$
B. $E{t}_{3}Al$
C. $C{H}_{2}C{H}_2$
D. $T{i}^{III}$

Answer 1

Hint: We know that in Ziegler-Natta polymerization, we Zeigler-Natta catalyst. A Zeigler-Natta catalyst contains two parts: a transition metal and an organoaluminum compound.

Complete step by step answer:
A catalyst that is used in the synthesis of polymers of 1-alkenes are Ziegler–Natta catalysts. We use Ziegler–Natta catalysts to polymerize terminal alkenes (ethylene and alkenes with the vinyl double bond). The reaction is written as,
$nC{H}_2=CHR\to -{\left[C{H}_2-CHR\right]}_n-$
There are two broad classes of Ziegler–Natta catalysts differentiated by their solubility:
We can use heterogeneous supported catalysts that are based on titanium compounds in polymerization reactions together with co catalysts. Cocatalysts are organoaluminum compounds like triethylaluminium $$Al{\left(C_2{H}_5\right)}_3$$.
Homogeneous catalysts that are based on complexes of Ti, Zr or Hf. We use homogeneous catalysts in combination with organoaluminum cocatalysts like methylaluminoxane.
Generally, Ziegler–Natta catalysts are produced by the action of $$Al{\left(C_2{H}_5\right)}_3$$ and $TiC{l}_4$. The active species is $T{i}^{III}$ because $$Al{\left(C_2{H}_5\right)}_3$$ could reduce $TiC{l}_4$ to form $TiC{l}_3$. An active site that is vacant is $T{i}^{III}$ and it could accommodate one alkyl group.

Zeigler-Natta catalysts do not work with acrylic substrates and Zeigler-Natta catalysts are not used in polymerization of vinyl chloride. It also does not work for monomers like 1,2-disubstituted double bonds.
An advantage of Ziegler-Natta catalysts is that this catalyst could yield an alpha-olefin polymer with controllable and high molecular weight. This catalyst makes the fabrication of polymers with specific tacticity possible. We can achieve polymers by controlling the stereochemistry of the products.

So, the correct answer is Option D.

Note:
We can prepare commercial polymers using Ziegler-Natta catalysts. Some of the commercial polymer synthesized using Ziegler-Natta catalysts are:
Polypropylene
Polyethylene
Polybutene-1
Polybutadiene
Polyacetylene
Polyisoprene