The present invention describes a process for making CF3CH═CHF (HFO-1234ze). The process involves the addition of carbon tetrachloride (CCl4) to 1,2-dichloroethylene to form CCl3CHClCHCl2. The compound CCl3CHClCHCl2 thus can then either be treated with HF to produce CF3CHClCHClF as the main product, or it can be converted to CCl2═CHCHCl2 (1230za) by dechlorination. CCl2═CHCHCl2 can be treated with HF such that the main product obtained is CF3CHClCHClF. CF3CH═CHCl may be produced as a by-product, but upon treatment with HF, it affords the compound CF3CHClCHClF. The desired compound, CF3CH═CHF (HFO-1234ze), is obtained as a trans/cis mixture by dehydrochlorination of CF3CH2CHClF or by dechlorination of CF3CHClCHClF.