Difference Between DEHT and DEHP

The key difference between DEHT and DEHP is that DEHT is a non-phthalate plasticizer, whereas DEHP is a phthalate plasticizer.

The terms DEHT and DEHP stand for two types of polymer materials which can be categorized as plasticizers. A plasticizer is a component we can add to a certain substance to increase the plasticity by softening and increasing the flexibility of that substance.

1. Overview and Key Difference
2. What is DEHT
3. What is DEHP
4. Side by Side Comparison – DEHT vs DEHP in Tabular Form
5. Summary

What is DEHT

The term DEHT stands for dioctyl terephthalate. Sometimes it is also abbreviated as DOTP. We can categorize it as a non-phthalate plasticizer. It is an organic compound having the chemical formula C₆H₄(CO₂C₈H₁₇)₂. This compound has two carboxylate groups at the para position of a benzyl ring. It is, therefore, a diester of terephthalic acid and it has two 2-ethylhexanol branched chains attached to the carboxylate group.

Figure 01: Chemical Structure of DEHT

DEHT occurs as a colourless, viscous liquid. Since it is a type of plasticizer, we can use this liquid for the softening of polymers such as PVC plastics. Therefore, in the general-purpose, DEHT is similar to DEHP and other phthalates, but the action of softening using DEHT can be done with negative regulatory pressure, which is an advantage. DEHT has valuable plasticizing properties, so we can use it for the direct replacement of DEHP in many applications.

There are two methods to manufacture DEHT: transesterification of dimethyl terephthalate with 2-ethylhexanol and direct esterification of terephthalic acid with 2-ethylhexanol. The transesterification process produces a byproduct: methanol, which can be purified to get pure methanol to be used in other applications. However, in the direct esterification method, the byproduct is water. Therefore, the second method is more environmentally friendly.

What is DEHP?

The term DEHP stands for dioctyl phthalate. It is an organic compound having the chemical formula C₆H₄(CO₂C₈H₁₇)₂. It is a common phthalate plasticizer. When considering the chemical structure of DEHP, it has two carboxylate groups in the ortho position of a benzyl ring. Therefore, we can recognize it as a diester of phthalic acid. It has two-branched chains of 2-ethylhexanol. DEHP occurs as a colourless and a viscous liquid at room temperature. It can dissolve in oil but cannot dissolve in water.

Figure 02: Chemical Structure of DEHP

DEHP has favourable properties and low cost to be used as a plasticizer. It is a common phthalic plasticizer. Usually, plastics such as PVC contain 1-40% DEHP blended with other components. This polymer material is also used as a hydraulic fluid, and it is an important dielectric fluid in capacitors. The most common way of producing DEHP is the reaction between phthalic anhydride with 2-ethylhexanol.

What is the Difference Between DEHT and DEHP?

The term DEHT stands for dioctyl terephthalate, while the term DEHP stands for dioctyl phthalate. The key difference between DEHT and DEHP is that DEHT is a non-phthalate plasticizer, whereas DEHP is a phthalate plasticizer. Besides, the structural difference between DEHT and DEHP is that DEHT has its carboxylate groups at the para position of a benzyl ring while DEHP has its two carboxylate groups at the ortho position of a benzyl ring.

Moreover, DEHT is less toxic than DEHP, so DEHT is used as a replacement for DEHP.

Below infographic summarizes the difference between DEHT and DEHP.

Summary – DEHT vs DEHP

DEHT and DEHP are important plasticizing agents. DEHT stands for dioctyl terephthalate while DEHP stands for dioctyl phthalate. The key difference between DEHT and DEHP is that DEHT is a non-phthalate plasticizer whereas DEHP is a phthalate plasticizer.

Reference:

1. “Dioctyl Terephthalate.” Wikipedia, Wikimedia Foundation, 2 June 2020, Available here.
2. “Bis(2-Ethylhexyl) Phthalate.” Wikipedia, Wikimedia Foundation, 30 Apr. 2020, Available here.

Image Courtesy:

1. “Dioctyl terephthalate” By Ed (Edgar181) – Own work (Public Domain) via Commons Wikimedia
2. “Bis(2-ethylhexyl) phthalate” By Dschanz – Own work using: BKchem (Public Domain) via Commons Wikimedia